[x86] replace integer 'xor' ops with packed SSE FP 'xor' ops when operating on FP scalars

Turn this:

movd %xmm0, %eax
movd %xmm1, %ecx
xorl %eax, %ecx
movd %ecx, %xmm0

into this:

xorps %xmm1, %xmm0

This is related to, but does not solve:
https://llvm.org/bugs/show_bug.cgi?id=22428

This is an extension of:
http://reviews.llvm.org/rL248395

llvm-svn: 248415