Rename PPC MTCTRse to MTCTRloop

As the pairing of this instruction form with the bdnz/bdz branches is now
enforced by the verification pass, make it clear from the name that these
are used only for counter-based loops.

No functionality change intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182296 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed