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/el3_runtime/context_mgmt.h b/include/lib/el3_runtime/context_mgmt.h
index f23f9cd..7c996d1 100644
--- a/include/lib/el3_runtime/context_mgmt.h
+++ b/include/lib/el3_runtime/context_mgmt.h
@@ -35,7 +35,7 @@
 void cm_setup_context(cpu_context_t *ctx, const entry_point_info_t *ep);
 void cm_prepare_el3_exit(uint32_t security_state);
 
-#ifndef AARCH32
+#ifdef __aarch64__
 void cm_el1_sysregs_context_save(uint32_t security_state);
 void cm_el1_sysregs_context_restore(uint32_t security_state);
 void cm_set_elr_el3(uint32_t security_state, uintptr_t entrypoint);
@@ -78,6 +78,6 @@
 #else
 void *cm_get_next_context(void);
 void cm_set_next_context(void *context);
-#endif /* AARCH32 */
+#endif /* __aarch64__ */
 
 #endif /* CONTEXT_MGMT_H */