[X86] Teach EltsFromConsecutiveLoads that it's ok to form a v4f32 VZEXT_LOAD...

[X86] Teach EltsFromConsecutiveLoads that it's ok to form a v4f32 VZEXT_LOAD with a 64 bit memory size on SSE1 targets.

We can use MOVLPS which will load 64 bits, but we need a v4f32
result type. We already have isel patterns for this.

The code here is a little hacky. We can probably improve it with
more isel patterns.