Fix MISRA rule 8.4 in common code

Rule 8.4: A compatible declaration shall be visible when
          an object or function with external linkage is defined.

Change-Id: I26e042cb251a6f9590afa1340fdac73e42f23979
Signed-off-by: Roberto Vargas <roberto.vargas@arm.com>
diff --git a/bl2/aarch64/bl2_arch_setup.c b/bl2/aarch64/bl2_arch_setup.c
index 038a075..54052f7 100644
--- a/bl2/aarch64/bl2_arch_setup.c
+++ b/bl2/aarch64/bl2_arch_setup.c
@@ -1,11 +1,12 @@
 /*
- * Copyright (c) 2013-2014, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2018, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
 #include <arch.h>
 #include <arch_helpers.h>
+#include "../bl2_private.h"
 
 /*******************************************************************************
  * Place holder function to perform any S-EL1 specific architectural setup. At