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/xilinx/zynqmp/ipi_mailbox_service/ipi_mailbox_svc.h b/plat/xilinx/zynqmp/ipi_mailbox_service/ipi_mailbox_svc.h
index 387ffd2..197c788 100644
--- a/plat/xilinx/zynqmp/ipi_mailbox_service/ipi_mailbox_svc.h
+++ b/plat/xilinx/zynqmp/ipi_mailbox_service/ipi_mailbox_svc.h
@@ -6,8 +6,8 @@
 
 /* ZynqMP IPI mailbox doorbell service enums and defines */
 
-#ifndef _IPI_MAILBOX_SVC_H_
-#define _IPI_MAILBOX_SVC_H_
+#ifndef IPI_MAILBOX_SVC_H
+#define IPI_MAILBOX_SVC_H
 
 #include <stdint.h>
 
@@ -36,4 +36,4 @@
 			 uint64_t x3, uint64_t x4, void *cookie, void *handle,
 			 uint64_t flags);
 
-#endif /* _IPI_MAILBOX_SVC_H_ */
+#endif /* IPI_MAILBOX_SVC_H */