[llvm][ARM] Missing switch statement handles (#116086)

PR #115153 added enums which needed to be handled in a switch statement.
This trips up buildbot.

Author: nasherm

llvm/lib/Target/ARM/ARMSubtarget.cpp

@@ -292,7 +292,9 @@ void ARMSubtarget::initSubtargetFeatures(StringRef CPU, StringRef FS) {
   case CortexR5:
   case CortexR7:
   case CortexM3:
+  case CortexM55:
   case CortexM7:
+  case CortexM85:
   case CortexR52:
   case CortexR52plus:
   case CortexX1: