[X86] Don't use Expand for i32 fp_to_uint on SSE1/2 targets on 32-bit target.

Use Custom lowering instead. Fall back to default expansion only
when the scalar FP type belongs in an XMM register. This improves
lowering for i32 to fp80, and also i32 to double on SSE1 only.

llvm-svn: 370699