AMDGPU: Generate VALU ThreeOp Integer instructions

Summary:
Original patch by: Fabian Wahlster <razor@singul4rity.com>

Change-Id: I148f692a88432541fad468963f58da9ddf79fac5

Reviewers: arsenm, rampitec

Subscribers: kzhuravl, jvesely, wdng, yaxunl, dstuttard, tpr, t-tye, b-sumner, llvm-commits

Differential Revision: https://reviews.llvm.org/D51995

llvm-svn: 348488