[X86] Add disassembler test cases for bswap.

This demonstrates a bug where the encoding for a 16-bit bswap prints a 16-bit register and a 32-bit mnemonic. Intel docs say 16-bit bswap is undefined. We should either claim it as an invalid encoding or we should print a 16-bit mnemonic.

objdump does print the encoding as bswap with a 16-bit register. But it doesn't seem to ever print a suffix.

llvm-svn: 330621