[X86][SSE] Add initial support for 2 input target shuffle combining.

At the moment only the INSERTPS matching can actually use 2 inputs but the plumbing is now in place.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@277839 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed