[X86] Don't fail disassembly if REX.R/REX.B is used on an MMX register. Similar fix to not fail to disassembler CR9-CR15 references.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224861 91177308-0d34-0410-b5e6-96231b3b80d8
[X86] Add the debug registers DR8-DR15 so we can assemble and disassemble references to them.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224862 91177308-0d34-0410-b5e6-96231b3b80d8