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/rockchip/rk3399/drivers/dp/cdn_dp.h b/plat/rockchip/rk3399/drivers/dp/cdn_dp.h
index 3b9a108..c5cbae2 100644
--- a/plat/rockchip/rk3399/drivers/dp/cdn_dp.h
+++ b/plat/rockchip/rk3399/drivers/dp/cdn_dp.h
@@ -4,8 +4,9 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
-#ifndef __SOC_ROCKCHIP_RK3399_DP_H__
-#define __SOC_ROCKCHIP_RK3399_DP_H__
+#ifndef CDN_DP_H
+#define CDN_DP_H
+
 #include <plat_private.h>
 
 enum {
@@ -44,4 +45,5 @@
 			   uint64_t x4,
 			   uint64_t x5,
 			   uint64_t x6);
-#endif
+
+#endif /* CDN_DP_H */