ART: Extract JNI macro assembler for arm

Extract the JNI assembler parts from the regular assembler.

Change-Id: Ice39ffeb854f8651e93443dd69f4c9e0e802975c
Test: m test-art-target (N6)
diff --git a/compiler/Android.mk b/compiler/Android.mk
index 16a158c..7a64678 100644
--- a/compiler/Android.mk
+++ b/compiler/Android.mk
@@ -98,6 +98,7 @@
 	utils/arm/assembler_arm.cc \
 	utils/arm/assembler_arm32.cc \
 	utils/arm/assembler_thumb2.cc \
+	utils/arm/jni_macro_assembler_arm.cc \
 	utils/arm/managed_register_arm.cc \
 
 # TODO We should really separate out those files that are actually needed for both variants of an