Clear upper parts of register in scalar [su]cvtf simulation

Scalar SIMD operations that write b, h, s or d registers should set the upper
parts of the destination register to zero. Fix the scvtf and ucvtf instructions
and add tests for all SISD instructions.
diff --git a/test/test-trace-reference/log-state b/test/test-trace-reference/log-state
index b495bfe..adad051 100644
--- a/test/test-trace-reference/log-state
+++ b/test/test-trace-reference/log-state
@@ -861,8 +861,8 @@
 #             d5:                 0x3f90000000000000
 #            d16:                 0x0000000000000000
 #            d15:                 0x0000000000000000
-#             v7: 0x00000000000000007ff000004e81442e
-#             v8: 0x0000000000000000c004000000000000
+#             v7: 0x0000000000000000000000004e81442e
+#             v8: 0x00000000000000000000000000000000
 #            s29:                         0x00000000
 #            s15:                         0x49800000
 #            s27:                         0x00000000
@@ -873,14 +873,14 @@
 #             d3:                 0x0000000000000000
 #            d28:                 0x41dfffffffc00000
 #            d27:                 0x0000000000000000
-#            v11: 0x0000000000000000400000004f7fe000
-#             v0: 0x000000000000000043d21c00480a8294
+#            v11: 0x0000000000000000000000004f7fe000
+#             v0: 0x000000000000000000000000480a8294
 #            s20:                         0x00000000
 #            s21:                         0x00000000
 #             s6:                         0x5f000000
 #             s7:                         0x38ff0000
-#            v19: 0x000000000000000043d21c00480a8294
-#            v16: 0x0000000000000000400000004f7f2000
+#            v19: 0x000000000000000000000000480a8294
+#            v16: 0x0000000000000000000000004f7f2000
 #             v0: 0x00000000000000000000000000000000
 #            v27: 0x00000000000000000000000000000000
 #            v21: 0x00000000000000000000000000000000
@@ -890,59 +890,59 @@
 #            v10: 0x00000000000000003f0000007f600000
 #            v31: 0x495000018a83940149500000d3029400
 #            v10: 0x495000018a83940168a6954c14cfd693
-#            v15: 0x00000000000000006328b14b89d7c527
+#            v15: 0x00000000000000001f56954b89d7c527
 #            v27: 0x0000000000000000495000000a029400
 #            v25: 0x000000000000000041efffffffc00000
 #            v13: 0x00000000000000000000000037feffff
 #             v4: 0x00000000000000000000000000000000
-#            v10: 0x000000000000000000000000827f4696
+#            v10: 0x0000000000000000000000003ead2a96
 #            v10: 0x00000000000000000000000000003c7f
 #            v31: 0x0000000000000000000000000000ffff
 #            v16: 0x00000000000000000000000000000000
 #             v0: 0x00000000000000000000000000000000
 #            v31: 0x000000000000b87f000000000000ffff
-#            v14: 0x000000000000000043d21c00480a8294
-#             v3: 0x0000000020febf0000000000c4000000
+#            v14: 0x000000000000000000000000480a8294
+#             v3: 0x0000000020febf000000000000000000
 #             v8: 0x000000007f8000003effffffffe00000
 #            v22: 0x00000000000000003c7fffff00000000
-#            v29: 0x00000000000000005fd2ca9e00000000
+#            v29: 0x00000000000000000000ca9e00000000
 #            v30: 0x0000000000000000000000003c7fffff
 #            v12: 0x0000000000000000000037000000bbfe
 #            v17: 0x000000003700bbfe00007f803efeffe0
 #            v27: 0x00000000000000000000000000000075
 #            v12: 0x00000000000000000000000000000000
 #            v27: 0x00000000000000000000000000003c7e
-#            v19: 0x00000000000000000000000000002a70
+#            v19: 0x0000000000000000000000000000ca9e
 #            v14: 0x00000000000000000000000000003c7e
 #            v10: 0x00000000000000000000000000000000
 #             v5: 0x00000000000000000000000000000000
-#            v26: 0x0000000020febf0000000000c4000000
+#            v26: 0x0000000020febf000000000000000000
 #             v7: 0x000000000000000000000000381b0000
 #            v28: 0x000000000000000040dfdcffdcc00000
-#            v29: 0x00000000000000005fd2ca1200000000
+#            v29: 0x00000000000000000000ca1200000000
 #            v12: 0x0000000000000000000000000000ffff
 #            v18: 0x000000000000000000000000ff67ff67
 #            v12: 0x00000000007ebf000000000000000000
 #             v2: 0x0000000000000000495000008a828000
-#             v8: 0x000000007f8000003effffffcc000000
+#             v8: 0x000000007f8000003effffffc8000000
 #             v5: 0x00000000000000000000000000000000
 #             v9: 0x0100000008009801010000000800dc00
-#            v14: 0x000000000000000000000000c4000000
+#            v14: 0x00000000000000000000000000000000
 #            v29: 0x07070707070707070707070707070707
 #            v21: 0x00000000000000000000001f0000001f
 #             v1: 0x0000000000000000000f000f000f000f
 #            v27: 0x0000001f0000001f0000001f0000001f
 #            v19: 0x00000000000000000707070707070707
-#            v15: 0x000f000f000f000f000f000f0001000f
+#            v15: 0x000f000f000f000f000f000f000f000f
 #             v1: 0x08080808080808080808080808080808
 #            v27: 0x00000000000000000000001100000002
 #             v9: 0x00000000000000000007001000040000
-#            v31: 0x0000000c0000000c0000000c0000000f
+#            v31: 0x0000000c0000000c0000000c0000000c
 #            v14: 0x00000000000000000505050505050505
-#             v6: 0x00100010001000100001001000010000
+#             v6: 0x00100010001000100010001000010000
 #            v18: 0x00000000000000000000000000000000
 #            v14: 0x00000000000000000000000000000000
-#            v19: 0xffffffff000000ff0000000000ffffff
+#            v19: 0xffffffff000000ff00000000ffffffff
 #            v15: 0xffffffffffffffffff00ff00ff00ffff
 #            v12: 0xffffffffffffffffffffffffffffffff
 #             v8: 0xffffffffffffffff0000000000000000
@@ -962,11 +962,11 @@
 #            v22: 0xffffffffffffffffffffffffffff0000
 #            v28: 0x0000000000000000ffffffffffffffff
 #             v6: 0xffffffffffffffffffffffffffffffff
-#            v25: 0x000000000000000000000000ffffffff
+#            v25: 0x00000000000000000000000000000000
 #            v21: 0x0000000000000000ffffffffffffffff
-#            v16: 0x0000000000000000ffffffff0000ffff
+#            v16: 0x0000000000000000ffffffffffffffff
 #            v23: 0x0000000000000000ffffffffffffffff
-#             v7: 0xffffffffffffffff0000000000000000
+#             v7: 0xffffffffffffffffffffffff00000000
 #             v0: 0x00000000000000000000000000000000
 #            v10: 0x0000000000000000ff00ff00ffff0000
 #            v21: 0x0000000000000000ffffffffffffffff
@@ -982,9 +982,9 @@
 #            v12: 0x00000000000000000000000000000000
 #            v28: 0x0000000000000000000000000000ffff
 #            v22: 0x00000000000000000000000000000000
-#             v5: 0x0000000000000000ffffffffffffffff
+#             v5: 0x000000000000000000000000ffffffff
 #            v13: 0x00000000000000000000000000000000
-#            v27: 0x0000000000000000000000ff000000ff
+#            v27: 0x0000000000000000ffffffff000000ff
 #             v5: 0x00000000000000000000000000000000
 #            v22: 0x00000000000000000000000000000000
 #             v6: 0x00000000000000000000000000000000
@@ -995,7 +995,7 @@
 #            v31: 0x00000000000000000000000000000000
 #             v9: 0x00000000000000000000000000000000
 #             v7: 0x00000000000000000000000000000000
-#            v11: 0x0000000000000000ffffffff00000000
+#            v11: 0x0000000000000000ffffffffffff0000
 #             v1: 0x00000000000000000000000000000000
 #            v21: 0xffffffffffffffffffffffffffffffff
 #             v8: 0xffffffffffffffffffffffffffffffff
@@ -1016,9 +1016,9 @@
 #             v7: 0x0000000000000000ffffffffffffffff
 #             v7: 0x0000000000000000ffffffffffffffff
 #            v25: 0x00000000000000000000000000000000
-#             v0: 0x0000000000000000ffffffff00000000
+#             v0: 0x0000000000000000ffffffffffff0000
 #            v24: 0x00000000000000000000000000000000
-#            v26: 0x0000000000000000ffffffff00000000
+#            v26: 0x0000000000000000ffffffffffff0000
 #             v1: 0x0000000000000000ffffffffffffffff
 #            v28: 0x0000000000000000ffffffffffffffff
 #            v26: 0x00000000000000000000000000000000
@@ -5244,7 +5244,7 @@
 #             v9: 0x43dfe000001fe0000000000000000000
 #            v26: 0x000000000000000040fff00000200000
 #            v11: 0x00000000000000000000000000000000
-#            v29: 0x7fc000007fc000000000000000000000
+#            v29: 0x00000000000000000000000000000000
 #            v22: 0x4effe000000000004e001a4000000000
 #            v18: 0x4207bfc03d7f00000000000000000000
 #       p8<15:0>: 0b 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 <- 0x~~~~~~~~~~~~~~~~