Use the new instruction deprecation feature to mark mftb (now replaced with
mfspr) and dst (along with the other Altivec cache control instructions) as
deprecated when targeting cores supporting at least ISA v2.03.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190605 91177308-0d34-0410-b5e6-96231b3b80d8
