Mark PPC MFTB and DST (and friends) as deprecated

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

lib/Target/PowerPC/PPCSubtarget.cpp

@@ -90,6 +90,8 @@ void PPCSubtarget::initializeEnvironment() {
   HasPOPCNTD = false;
   HasLDBRX = false;
   IsBookE = false;
+  DeprecatedMFTB = false;
+  DeprecatedDST = false;
   HasLazyResolverStubs = false;
   IsJITCodeModel = false;
 }