R600/SI: Implement SIInstrInfo::verifyInstruction() for VOP*

The function is used by the machine verifier and checks that VOP*
instructions have legal operands.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192367 91177308-0d34-0410-b5e6-96231b3b80d8