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/hisilicon/hikey960/include/hi3660_hkadc.h b/plat/hisilicon/hikey960/include/hi3660_hkadc.h
index 6e67114..4d2de4a 100644
--- a/plat/hisilicon/hikey960/include/hi3660_hkadc.h
+++ b/plat/hisilicon/hikey960/include/hi3660_hkadc.h
@@ -3,8 +3,8 @@
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
-#ifndef __HI3660_HKADC_H__
-#define __HI3660_HKADC_H__
+#ifndef HI3660_HKADC_H
+#define HI3660_HKADC_H
 
 #define HKADC_SSI_REG_BASE			0xE82B8000
 
@@ -58,4 +58,4 @@
 #define START_DELAY_TIMEOUT			2000
 #define HKADC_WR_NUM_VALUE			4
 
-#endif /* __HI3660_HKADC_H__ */
+#endif /* HI3660_HKADC_H */