[X86][SSE] Introduce Float/Vector WriteMove, WriteLoad and Writetore scheduler classes

As discussed on D44428 and PR36726, this patch splits off WriteFMove/WriteVecMove, WriteFLoad/WriteVecLoad and WriteFStore/WriteVecStore scheduler classes to permit vectors to be handled separately from gpr/scalar types.

I've minimised the diff here by only moving various basic SSE/AVX vector instructions across - we can fix the rest when called for. This does fix the MOVDQA vs MOVAPS/MOVAPD discrepancies mentioned on D44428.

Differential Revision: https://reviews.llvm.org/D44471

llvm-svn: 327630