[X86][Disassembler] Add bizarro versions of the MOVSXD instruction that sign...

[X86][Disassembler] Add bizarro versions of the MOVSXD instruction that sign extend from a GR32 to GR32 or GR16.

The 0x63 opcodes in 64-bit mode have a fixed source size of 32-bits, but the destination size is controlled by REX.W and the 0x66 opsize prefix. This instruction is normally used with a REX.W prefix which provides desired behavior. The other encodings are interpretted as valid by the processor, but aren't useful.

This patch makes us recognize them for the disassembler to match objdump.

llvm-svn: 343614