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/drivers/marvell/gwin.h b/include/drivers/marvell/gwin.h
index 5dc9f24..6b7f175 100644
--- a/include/drivers/marvell/gwin.h
+++ b/include/drivers/marvell/gwin.h
@@ -7,8 +7,8 @@
 
 /* GWIN unit device driver for Marvell AP810 SoC */
 
-#ifndef _GWIN_H_
-#define _GWIN_H_
+#ifndef GWIN_H
+#define GWIN_H
 
 #include <addr_map.h>
 
@@ -16,4 +16,4 @@
 void gwin_temp_win_insert(int ap_index, struct addr_map_win *win, int size);
 void gwin_temp_win_remove(int ap_index, struct addr_map_win *win, int size);
 
-#endif /* _GWIN_H_ */
+#endif /* GWIN_H */