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/libpixelflinger/codeflinger/ARMAssemblerInterface.h b/libpixelflinger/codeflinger/ARMAssemblerInterface.h
index 6e0d7c6..40cbfcf 100644
--- a/libpixelflinger/codeflinger/ARMAssemblerInterface.h
+++ b/libpixelflinger/codeflinger/ARMAssemblerInterface.h
@@ -63,7 +63,7 @@
     };
 
     enum {
-        CODEGEN_ARCH_ARM = 1, CODEGEN_ARCH_MIPS, CODEGEN_ARCH_AARCH64
+        CODEGEN_ARCH_ARM = 1, CODEGEN_ARCH_MIPS, CODEGEN_ARCH_ARM64
     };
 
     // -----------------------------------------------------------------------