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_io_mux.h b/plat/imx/common/include/imx_io_mux.h
index 44284f6..9b30421 100644
--- a/plat/imx/common/include/imx_io_mux.h
+++ b/plat/imx/common/include/imx_io_mux.h
@@ -4,8 +4,8 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
-#ifndef __IMX_IO_MUX_H__
-#define __IMX_IO_MUX_H__
+#ifndef IMX_IO_MUX_H
+#define IMX_IO_MUX_H
 
 #include <stdint.h>
 
@@ -606,4 +606,4 @@
 void imx_io_muxc_set_pad_alt_function(uint32_t pad_mux_offset, uint32_t alt_function);
 void imx_io_muxc_set_pad_features(uint32_t pad_feature_offset, uint32_t pad_features);
 
-#endif /* __IMX_IO_MUX_H__ */
+#endif /* IMX_IO_MUX_H */