Switch AARCH32/AARCH64 to __aarch64__

NOTE: AARCH32/AARCH64 macros are now deprecated in favor of __aarch64__.

All common C compilers pre-define the same macros to signal which
architecture the code is being compiled for: __arm__ for AArch32 (or
earlier versions) and __aarch64__ for AArch64. There's no need for TF-A
to define its own custom macros for this. In order to unify code with
the export headers (which use __aarch64__ to avoid another dependency),
let's deprecate the AARCH32 and AARCH64 macros and switch the code base
over to the pre-defined standard macro. (Since it is somewhat
unintuitive that __arm__ only means AArch32, let's standardize on only
using __aarch64__.)

Change-Id: Ic77de4b052297d77f38fc95f95f65a8ee70cf200
Signed-off-by: Julius Werner <jwerner@chromium.org>
diff --git a/include/lib/xlat_tables/xlat_tables_arch.h b/include/lib/xlat_tables/xlat_tables_arch.h
index 7237534..0ce0cac 100644
--- a/include/lib/xlat_tables/xlat_tables_arch.h
+++ b/include/lib/xlat_tables/xlat_tables_arch.h
@@ -7,10 +7,10 @@
 #ifndef XLAT_TABLES_ARCH_H
 #define XLAT_TABLES_ARCH_H
 
-#ifdef AARCH32
-#include "aarch32/xlat_tables_aarch32.h"
-#else
+#ifdef __aarch64__
 #include "aarch64/xlat_tables_aarch64.h"
+#else
+#include "aarch32/xlat_tables_aarch32.h"
 #endif
 
 /*