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__.)

NOTE: This change is based on below TFA commit
https://github.com/ARM-software/arm-trusted-firmware/commit/402b3cf8766fe2cb4ae462f7ee7761d08a1ba56c

Signed-off-by: Deepika Bhavnani <deepika.bhavnani@arm.com>
Change-Id: If2c3dbaeb01d4a9d8cfd95d906e5eaf4ae94417f
diff --git a/include/lib/utils_def.h b/include/lib/utils_def.h
index 02963ac..78d4131 100644
--- a/include/lib/utils_def.h
+++ b/include/lib/utils_def.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2016-2020, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -19,7 +19,7 @@
 #define BIT_32(nr)			(U(1) << (nr))
 #define BIT_64(nr)			(ULL(1) << (nr))
 
-#ifdef AARCH32
+#ifndef __aarch64__
 #define BIT				BIT_32
 #else
 #define BIT				BIT_64
@@ -44,7 +44,7 @@
 	(((~UINT64_C(0)) << (l)) & (~UINT64_C(0) >> (64 - 1 - (h))))
 #endif
 
-#ifdef AARCH32
+#ifndef __aarch64__
 #define GENMASK				GENMASK_32
 #else
 #define GENMASK				GENMASK_64
@@ -130,7 +130,7 @@
 #endif
 
 /* Register size of the current architecture. */
-#ifdef AARCH32
+#ifndef __aarch64__
 #define REGSZ		U(4)
 #else
 #define REGSZ		U(8)