system/core: rename aarch64 target to arm64

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

Change-Id: Ia92d8a50824e5329cf00fd6f4f92eae112b7f3a3
diff --git a/include/cutils/atomic-inline.h b/include/cutils/atomic-inline.h
index 29a28d5..ae79e00 100644
--- a/include/cutils/atomic-inline.h
+++ b/include/cutils/atomic-inline.h
@@ -44,7 +44,7 @@
 #endif
 
 #if defined(__aarch64__)
-#include <cutils/atomic-aarch64.h>
+#include <cutils/atomic-arm64.h>
 #elif defined(__arm__)
 #include <cutils/atomic-arm.h>
 #elif defined(__i386__) || defined(__x86_64__)