Added more insertps optimizations

Summary:
When inserting an element that's coming from a vector load or a broadcast
of a vector (or scalar) load, combine the load into the insertps
instruction.
Added PerformINSERTPSCombine for the case where we need to fix the load
(load of a vector + insertps with a non-zero CountS).
Added patterns for the broadcasts.

Also added tests for SSE4.1, AVX, and AVX2.

Reviewers: delena, nadav, craig.topper

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D3581