Implement monitorenter/monitorexit.

Pretty simple as they just invoke the runtime.

Change-Id: I5fcb2c783deac27e55e28d8b3da3e68ea4b77363
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index ac65c1d..95c2fe7 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -639,6 +639,7 @@
   M(LoadClass)                                             \
   M(LoadException)                                         \
   M(LoadString)                                            \
+  M(MonitorOperation)                                      \
   M(ParallelMove)                                          \
   M(StaticFieldGet)                                        \
   M(StaticFieldSet)                                        \