Add support for features up to Armv8.3.

This is a squashed merge of several separate patches that, combined, add support
for most architectural features described up to Armv8.3.

Change-Id: Ia67f25fb9b82d5968120b0b144bd232e1898dc90
diff --git a/src/cpu-features.h b/src/cpu-features.h
index e5c68ab..853421b 100644
--- a/src/cpu-features.h
+++ b/src/cpu-features.h
@@ -61,6 +61,8 @@
   /* Half-precision (FP16) support for FP and NEON, respectively.           */ \
   V(kFPHalf,              "FPHalf",                 "fphp")                    \
   V(kNEONHalf,            "NEONHalf",               "asimdhp")                 \
+  /* The RAS extension, including the ESB instruction.                      */ \
+  V(kRAS,                 "RAS",                    NULL)                      \
   /* Data cache clean to the point of persistence: DC CVAP.                 */ \
   V(kDCPoP,               "DCPoP",                  "dcpop")                   \
   /* Cryptographic support instructions.                                    */ \