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/plat/allwinner/sun50i_h6/include/sunxi_mmap.h b/plat/allwinner/sun50i_h6/include/sunxi_mmap.h
index ff1eb61..f36491a 100644
--- a/plat/allwinner/sun50i_h6/include/sunxi_mmap.h
+++ b/plat/allwinner/sun50i_h6/include/sunxi_mmap.h
@@ -4,8 +4,8 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
-#ifndef __SUNXI_MMAP_H__
-#define __SUNXI_MMAP_H__
+#ifndef SUNXI_MMAP_H
+#define SUNXI_MMAP_H
 
 /* Memory regions */
 #define SUNXI_ROM_BASE			0x00000000
@@ -58,4 +58,4 @@
 #define SUNXI_R_UART_BASE		0x07080000
 #define SUNXI_R_PIO_BASE		0x07022000
 
-#endif /* __SUNXI_MMAP_H__ */
+#endif /* SUNXI_MMAP_H */