R600/SI: Assume SIFixSGPRCopies makes changes

I'm not sure if this was breaking anything.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222174 91177308-0d34-0410-b5e6-96231b3b80d8
R600/SI: Don't copy flags when extracting subreg

This was resulting in use of a register after a kill.
For some reason this showed up as a problem in many tests
when moving the SIFixSGPRCopies pass closer to instruction
selection.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222175 91177308-0d34-0410-b5e6-96231b3b80d8