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/bl2/bl2.h b/include/bl2/bl2.h
new file mode 100644
index 0000000..89ff06e
--- /dev/null
+++ b/include/bl2/bl2.h
@@ -0,0 +1,12 @@
+/*
+ * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef BL2_H__
+#define BL2_H__
+
+void bl2_main(void);
+
+#endif /* BL2_H__ */