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/drivers/arm/gic/v2/gicv2_helpers.c b/drivers/arm/gic/v2/gicv2_helpers.c
index 0df50fb..421669f 100644
--- a/drivers/arm/gic/v2/gicv2_helpers.c
+++ b/drivers/arm/gic/v2/gicv2_helpers.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015-2017, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2018, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -9,6 +9,7 @@
 #include <assert.h>
 #include <debug.h>
 #include <gic_common.h>
+#include <gicv2.h>
 #include <interrupt_props.h>
 #include "../common/gic_common_private.h"
 #include "gicv2_private.h"