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/mediatek/mt8173/drivers/spm/spm_mcdi.h b/plat/mediatek/mt8173/drivers/spm/spm_mcdi.h
index e29f565..7f3f96e 100644
--- a/plat/mediatek/mt8173/drivers/spm/spm_mcdi.h
+++ b/plat/mediatek/mt8173/drivers/spm/spm_mcdi.h
@@ -3,12 +3,12 @@
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
-#ifndef __SPM_MCDI_H__
-#define __SPM_MCDI_H__
+#ifndef SPM_MCDI_H
+#define SPM_MCDI_H
 
 void spm_mcdi_wakeup_all_cores(void);
 void spm_mcdi_prepare_for_mtcmos(void);
 void spm_mcdi_prepare_for_off_state(unsigned long mpidr, unsigned int afflvl);
 void spm_mcdi_finish_for_on_state(unsigned long mpidr, unsigned int afflvl);
 
-#endif /* __SPM_MCDI_H__ */
+#endif /* SPM_MCDI_H */