py: Use mp_raise_TypeError/mp_raise_ValueError helpers where possible.

Saves 168 bytes on bare-arm.
diff --git a/py/parsenum.c b/py/parsenum.c
index 2e41801..1771188 100644
--- a/py/parsenum.c
+++ b/py/parsenum.c
@@ -55,7 +55,7 @@
     // check radix base
     if ((base != 0 && base < 2) || base > 36) {
         // this won't be reached if lex!=NULL
-        mp_raise_msg(&mp_type_ValueError, "int() arg 2 must be >= 2 and <= 36");
+        mp_raise_ValueError("int() arg 2 must be >= 2 and <= 36");
     }
 
     // skip leading space