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/common/desc_image_load.h b/include/common/desc_image_load.h
index 1ed2b15..6254895 100644
--- a/include/common/desc_image_load.h
+++ b/include/common/desc_image_load.h
@@ -3,8 +3,8 @@
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
-#ifndef __DESC_IMAGE_LOAD_H__
-#define __DESC_IMAGE_LOAD_H__
+#ifndef DESC_IMAGE_LOAD_H
+#define DESC_IMAGE_LOAD_H
 
 #include <bl_common.h>
 
@@ -37,4 +37,4 @@
 bl_params_t *get_next_bl_params_from_mem_params_desc(void);
 void populate_next_bl_params_config(bl_params_t *bl2_to_next_bl_params);
 
-#endif /* __DESC_IMAGE_LOAD_H__ */
+#endif /* DESC_IMAGE_LOAD_H */