art: rename aarch64 target to arm64

Rename aarch64 build targets to arm64.  The gcc toolchain is still
aarch64.

Change-Id: Ia92d8a50824e5329cf00fd6f4f92eae112b7f3a3
diff --git a/runtime/Android.mk b/runtime/Android.mk
index 237e930..9e6d5f9 100644
--- a/runtime/Android.mk
+++ b/runtime/Android.mk
@@ -230,11 +230,11 @@
 	arch/mips/quick_entrypoints_mips.S \
 	arch/mips/thread_mips.cc
 else # TARGET_ARCH != mips
-ifeq ($(TARGET_ARCH),aarch64)
-$(info TODOAArch64: $(LOCAL_PATH)/Android.mk Add AArch64 specific runtime files)
+ifeq ($(TARGET_ARCH),arm64)
+$(info TODOArm64: $(LOCAL_PATH)/Android.mk Add Arm64 specific runtime files)
 else
 $(error unsupported TARGET_ARCH=$(TARGET_ARCH))
-endif # TARGET_ARCH != aarch64
+endif # TARGET_ARCH != arm64
 endif # TARGET_ARCH != mips
 endif # TARGET_ARCH != x86_64
 endif # TARGET_ARCH != x86