include: add display fbcon function prototype

Add the prototype for display fbcon function.

Change-Id: Ic7f85034ea803d71a124548b6aee20194c8b7923
diff --git a/include/platform.h b/include/platform.h
index a513843..3cb7f2f 100644
--- a/include/platform.h
+++ b/include/platform.h
@@ -49,6 +49,7 @@
 void display_init(void);
 void display_shutdown(void);
 void display_image_on_screen(void);
+void display_fbcon_message(char *str);
 
 unsigned board_machtype(void);
 unsigned board_platform_id(void);