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/bl31/bl31.h b/include/bl31/bl31.h
index aac6e28..7c35922 100644
--- a/include/bl31/bl31.h
+++ b/include/bl31/bl31.h
@@ -18,5 +18,7 @@
 void bl31_prepare_next_image_entry(void);
 void bl31_register_bl32_init(int32_t (*func)(void));
 void bl31_warm_entrypoint(void);
+void bl31_main(void);
+void bl31_lib_init(void);
 
 #endif /* __BL31_H__ */