[X86] Stop accidentally custom type legalizing v4i32->v4f32 on SSE1 only targets.

We had a Custom operation action for v4i32 on SSE1. But since
v4i32 isn't legal until SSE2 this was not what was intended. The
code that get executed was intended for op legalization and
creates a bunch of v4i32 nodes that all end up scalarized.