Use the thumb2 assembler for the optimizing compiler.

Change-Id: I2b058f4433504dc3299c06f5cb0b5ab12f34aa82
diff --git a/compiler/utils/arm/assembler_arm.cc b/compiler/utils/arm/assembler_arm.cc
index 8a34928..5fe8246 100644
--- a/compiler/utils/arm/assembler_arm.cc
+++ b/compiler/utils/arm/assembler_arm.cc
@@ -169,9 +169,7 @@
       return ArmAssembler::ModifiedImmediate(immediate) != kInvalidModifiedImmediate;
 
     case MOV:
-      if (immediate < (1 << 12)) {    // Less than (or equal to) 12 bits can always be done.
-        return true;
-      }
+      // TODO: Support less than or equal to 12bits.
       return ArmAssembler::ModifiedImmediate(immediate) != kInvalidModifiedImmediate;
     case MVN:
     default: