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/bl31/bl31_main.c b/bl31/bl31_main.c
index a34cf86..0664741 100644
--- a/bl31/bl31_main.c
+++ b/bl31/bl31_main.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2017, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2018, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -17,6 +17,7 @@
 #include <pmf.h>
 #include <runtime_instr.h>
 #include <runtime_svc.h>
+#include <std_svc.h>
 #include <string.h>
 
 #if ENABLE_RUNTIME_INSTRUMENTATION