Standardise header guards across codebase

All identifiers, regardless of use, that start with two underscores are
reserved. This means they can't be used in header guards.

The style that this project is now to use the full name of the file in
capital letters followed by 'H'. For example, for a file called
"uart_example.h", the header guard is UART_EXAMPLE_H.

The exceptions are files that are imported from other projects:

- CryptoCell driver
- dt-bindings folders
- zlib headers

Change-Id: I50561bf6c88b491ec440d0c8385c74650f3c106e
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/include/lib/cpus/aarch64/cortex_a72.h b/include/lib/cpus/aarch64/cortex_a72.h
index 5b9e06d..4eafc11 100644
--- a/include/lib/cpus/aarch64/cortex_a72.h
+++ b/include/lib/cpus/aarch64/cortex_a72.h
@@ -4,8 +4,8 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
-#ifndef __CORTEX_A72_H__
-#define __CORTEX_A72_H__
+#ifndef CORTEX_A72_H
+#define CORTEX_A72_H
 #include <utils_def.h>
 
 /* Cortex-A72 midr for revision 0 */
@@ -61,4 +61,4 @@
  ******************************************************************************/
 #define CORTEX_A72_L2MERRSR_EL1				S3_1_C15_C2_3
 
-#endif /* __CORTEX_A72_H__ */
+#endif /* CORTEX_A72_H */