Remove extern keyword from function declarations

Function declarations implicitly have external linkage so do not
need the extern keyword.

Change-Id: Ia0549786796d8bf5956487e8996450a0b3d79f32
diff --git a/include/bl31/runtime_svc.h b/include/bl31/runtime_svc.h
index 66562e1..d7d88d4 100644
--- a/include/bl31/runtime_svc.h
+++ b/include/bl31/runtime_svc.h
@@ -264,10 +264,10 @@
 /*******************************************************************************
  * Function & variable prototypes
  ******************************************************************************/
-extern void runtime_svc_init();
+void runtime_svc_init();
 extern uint64_t __RT_SVC_DESCS_START__;
 extern uint64_t __RT_SVC_DESCS_END__;
-extern uint64_t get_crash_stack(uint64_t mpidr);
-extern void runtime_exceptions(void);
+uint64_t get_crash_stack(uint64_t mpidr);
+void runtime_exceptions(void);
 #endif /*__ASSEMBLY__*/
 #endif /* __RUNTIME_SVC_H__ */