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/include/common/runtime_svc.h b/include/common/runtime_svc.h
index e179e4b..6150b32 100644
--- a/include/common/runtime_svc.h
+++ b/include/common/runtime_svc.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2016, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2018, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -126,5 +126,7 @@
 extern uintptr_t __RT_SVC_DESCS_END__;
 void init_crash_reporting(void);
 
+extern uint8_t rt_svc_descs_indices[MAX_RT_SVCS];
+
 #endif /*__ASSEMBLY__*/
 #endif /* __RUNTIME_SVC_H__ */