TZC: rename included C file to a header

C files shouldn't be included into others. This file only contains some
macros and functions that can be made `static inline`, so it is ok to
convert it into a header file.

This is the only occurrence of a C file being included in another one in
the codebase instead of using a header, other occurrences are a way of
achieving backwards-compatibility.

Functions therein have been qualified as `inline`.

Change-Id: I88fe300f6d85a7f0740ef14c9cb8fa54849218e6
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/drivers/arm/tzc/tzc400.c b/drivers/arm/tzc/tzc400.c
index ca088c3..8c6f8ba 100644
--- a/drivers/arm/tzc/tzc400.c
+++ b/drivers/arm/tzc/tzc400.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2016-2017, ARM Limited and Contributors. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -33,7 +33,7 @@
 #include <mmio.h>
 #include <stddef.h>
 #include <tzc400.h>
-#include "tzc_common_private.c"
+#include "tzc_common_private.h"
 
 /*
  * Macros which will be used by common core functions.