R600/SI: Refactor fneg / fabs patterns

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215746 91177308-0d34-0410-b5e6-96231b3b80d8
R600/SI: Use source modifier for f64 fabs

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215747 91177308-0d34-0410-b5e6-96231b3b80d8
R600/SI: Use source modifiers for f64 fneg

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215748 91177308-0d34-0410-b5e6-96231b3b80d8
R600/SI: Move all fabs / fneg handling to patterns

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215749 91177308-0d34-0410-b5e6-96231b3b80d8