[X86][SSE] Keep 4i32 vector insertions in integer domain on SSE4.1 targets

4i32 shuffles for single insertions into zero vectors lowers to X86vzmovl which was using (v)blendps - causing domain switch stalls. This patch fixes this by using (v)pblendw instead.

The updated tests on test/CodeGen/X86/sse41.ll still contain a domain stall due to the use of insertps - I'm looking at fixing this in a future patch.

Differential Revision: http://reviews.llvm.org/D6458