[X86][SSE] Use pblendw for v4i32/v2i64 during isel.

Summary:

Previously we used BLENDPS/BLENDPD but that puts the blend in the FP domain. Under optsize, the two address instruction pass can cause blendps/blendpd to commute to blendps/blendpd. But we probably shouldn't do that if the original type was a integer. So use pblendw instead.

Reviewers: spatel, RKSimon

Reviewed By: RKSimon

Subscribers: jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58574

llvm-svn: 354755