[ARM] Diagnose ARM MOVT without :lower16: or :upper16: expression

This instruction was missing from the list of opcodes that we check, so we were
hitting an llvm_unreachable in ARMMCCodeEmitter.cpp for the ARM MOVT
instruction, rather than the diagnostic that is emitted for the other MOVW/MOVT
instructions.

Differential revision: https://reviews.llvm.org/D30936

llvm-svn: 297739
diff --git a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index f20ee1b..1a6f8e7 100644
--- a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -6682,6 +6682,7 @@
     break;
   }
   case ARM::MOVi16:
+  case ARM::MOVTi16:
   case ARM::t2MOVi16:
   case ARM::t2MOVTi16:
     {