R600/SI: Do abs/neg folding with ComplexPatterns

R600/SI: Do abs/neg folding with ComplexPatterns

Abs/neg folding has moved out of foldOperands and into the instruction
selection phase using complex patterns.  As a consequence of this
change, we now prefer to select the 64-bit encoding for most
instructions and the modifier operands have been dropped from
integer VOP3 instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214467 91177308-0d34-0410-b5e6-96231b3b80d8