[SystemZ] Rename PSW to CC

Addresses a review comment from Ulrich Weigand.  No functional change intended.

I'm not sure whether the old TODO that this patch touches still holds,
but that's something we'd get to when adding a targetted scheduling
description.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182474 91177308-0d34-0410-b5e6-96231b3b80d8