Fix MISRA rule 8.4 Part 1

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

Fixed for:
	make DEBUG=1 PLAT=fvp LOG_LEVEL=50 all

Change-Id: I7c2ad3f5c015411c202605851240d5347e4cc8c7
Signed-off-by: Roberto Vargas <roberto.vargas@arm.com>
diff --git a/drivers/arm/gic/v3/gicv3_main.c b/drivers/arm/gic/v3/gicv3_main.c
index 8de5be3..45a2e5b 100644
--- a/drivers/arm/gic/v3/gicv3_main.c
+++ b/drivers/arm/gic/v3/gicv3_main.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
  */
@@ -21,7 +21,7 @@
  * spinlock are used either at boot time (when only a single CPU is active), or
  * when the system is fully coherent.
  */
-spinlock_t gic_lock;
+static spinlock_t gic_lock;
 
 /*
  * Redistributor power operations are weakly bound so that they can be