[X86][Disassembler] Make sure EVEX.X is not used to extend base registers of memory operations.

This was an accidental side effect of EVEX.X being used to encode XMM16-XMM31 using modrm.rm with modrm.mod==0x3.

I think there are still more bugs related to this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@333722 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed