ARM: Make "SMC" instructions conditional on new TrustZone architecture feature.

These instructions aren't universally available, but depend on a specific
extension to the normal ARM architecture (rather than, say, v6/v7/...) so a new
feature is appropriate.

This also enables the feature by default on A-class cores which usually have
these extensions, to avoid breaking existing code and act as a sensible
default.

llvm-svn: 179171
diff --git a/llvm/lib/Target/ARM/ARMSubtarget.cpp b/llvm/lib/Target/ARM/ARMSubtarget.cpp
index 739300e..8653c46 100644
--- a/llvm/lib/Target/ARM/ARMSubtarget.cpp
+++ b/llvm/lib/Target/ARM/ARMSubtarget.cpp
@@ -91,6 +91,7 @@
   HasRAS = false;
   HasMPExtension = false;
   FPOnlySP = false;
+  HasTrustZone = false;
   AllowsUnalignedMem = false;
   Thumb2DSP = false;
   UseNaClTrap = false;