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/imx/common/include/imx_clock.h b/plat/imx/common/include/imx_clock.h
index 8558638..ce245ad 100644
--- a/plat/imx/common/include/imx_clock.h
+++ b/plat/imx/common/include/imx_clock.h
@@ -3,8 +3,8 @@
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
-#ifndef __IMX_CLOCK_H__
-#define __IMX_CLOCK_H__
+#ifndef IMX_CLOCK_H
+#define IMX_CLOCK_H
 
 #include <stdint.h>
 #include <stdbool.h>
@@ -999,4 +999,4 @@
 void imx_clock_disable_usb(unsigned int usb_id);
 void imx_clock_set_usb_clk_root_bits(uint32_t usb_clk_root_en_bits);
 
-#endif /* __IMX_CLOCK_H__ */
+#endif /* IMX_CLOCK_H */