[X86] Add a BSWAP16 instruction using the 32-bit encoding plus a 0x66 prefix.

This encoding is recognized by the CPU, but the behavior is undefined. This makes the disassembler handle it correctly so we don't print bswapl with a 16-bit register.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@330682 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed