[X86] Use sse_load_f32/f64 and timm in patterns for memory form of vgetmantss/sd.

Previously we only matched scalar_to_vector and scalar load, but
we should be able to narrow a vector load or match vzload.

Also need to match TargetConstant instead of Constant. The register
patterns were previously updated, but not the memory patterns.

llvm-svn: 372458