[X86] Redefine MOVSS/MOVSD instructions to take VR128 regclass as input instead of FR32/FR64

This patch redefines the MOVSS/MOVSD instructions to take VR128 as its second input. This allows the MOVSS/SD->BLEND commute to work without requiring a COPY to be inserted.

This should fix PR33079

Overall this looks to be an improvement in the generated code. I haven't checked the EXPENSIVE_CHECKS build but I'll do that and update with results.

Differential Revision: https://reviews.llvm.org/D38449

llvm-svn: 314914