[X86] Refactor PMOV[SZ]Xrm to add missing AVX2 patterns.

Most patterns will go away once the extload legalization changes land.

Differential Revision: http://reviews.llvm.org/D6125


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223567 91177308-0d34-0410-b5e6-96231b3b80d8