[Optimizing] Thumb2 assembler: use 16bits branches when we can.

We cannot relocate branches, but we can at least encode branches
on 16bits when the target is known.

Change-Id: Icb6116ed974fc97e03622ac80d914c2c06f4cba2
diff --git a/compiler/optimizing/code_generator_arm.cc b/compiler/optimizing/code_generator_arm.cc
index 7b37f74..1c76630 100644
--- a/compiler/optimizing/code_generator_arm.cc
+++ b/compiler/optimizing/code_generator_arm.cc
@@ -391,7 +391,7 @@
       location_builder_(graph, this),
       instruction_visitor_(graph, this),
       move_resolver_(graph->GetArena(), this),
-      assembler_(true),
+      assembler_(false /* can_relocate_branches */),
       isa_features_(isa_features) {
   // Save the PC register to mimic Quick.
   AddAllocatedRegister(Location::RegisterLocation(PC));