Implement byte swapping instructions on MIPS32 and MIPS64.

src/mips/constants-mips.h

Index: src/mips/constants-mips.h
diff --git a/src/mips/constants-mips.h b/src/mips/constants-mips.h
index f50a84927af4eeab18aa718f4bfa0023faa1a9ee..8301c5e5de29e7724e4a159c7fe2fc47cf544a8b 100644
--- a/src/mips/constants-mips.h
+++ b/src/mips/constants-mips.h
@@ -1186,11 +1186,10 @@ Instruction::Type Instruction::InstructionType(TypeChecks checks) const {
           int sa = SaFieldRaw() >> kSaShift;
           switch (sa) {
             case BITSWAP:
-              return kRegisterType;
             case WSBH:
             case SEB:
             case SEH:
-              return kUnsupported;
+              return kRegisterType;
           }
           sa >>= kBp2Bits;
           switch (sa) {