[X86] Type legalize v2f32 stores by widening to v4f32, casting to v2f64, extracting...

[X86] Type legalize v2f32 stores by widening to v4f32, casting to v2f64, extracting f64 and storing.

Summary: This is similar to what D52528 did for loads. It should match what generic type legalization does in 64-bit mode where it uses a v2i64 cast and an i64 store.

Reviewers: RKSimon, spatel

Reviewed By: RKSimon

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D53173

llvm-svn: 344470