[X86] Remove 64/128/256 from MMX/SSE/AVX instruction names for overall consistency. NFC

MMX instrutions all start with MMX_ so the 64 isn't needed for disambigutation.
SSE/AVX1 instructions are assumed 128-bit so we don't need to say 128.
AVX2 instructions should use a Y to indicate 256-bits.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@323402 91177308-0d34-0410-b5e6-96231b3b80d8
10 files changed