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>

common/backtrace/backtrace.c

@@ -93,7 +93,7 @@ static const char *get_el_str(unsigned int el)
  * Returns true if the address points to a virtual address that can be read at
  * the current EL, false otherwise.
  */
-#ifdef AARCH64
+#ifdef __aarch64__
 static bool is_address_readable(uintptr_t addr)
 {
 	unsigned int el = get_current_el();
@@ -123,7 +123,7 @@ static bool is_address_readable(uintptr_t addr)
 
 	return true;
 }
-#else /* if AARCH32 */
+#else /* !__aarch64__ */
 static bool is_address_readable(uintptr_t addr)
 {
 	unsigned int el = get_current_el();
@@ -144,7 +144,7 @@ static bool is_address_readable(uintptr_t addr)
 
 	return true;
 }
-#endif
+#endif /* __aarch64__ */
 
 /*
  * Returns true if all the bytes in a given object are in mapped memory and an
@@ -207,7 +207,7 @@ static bool is_valid_frame_record(struct frame_record *fr)
  */
 static struct frame_record *adjust_frame_record(struct frame_record *fr)
 {
-#ifdef AARCH64
+#ifdef __aarch64__
 	return fr;
 #else
 	return (struct frame_record *)((uintptr_t)fr - 4U);