board_f: initcall: Add a header guard

This file is missing the usual header guard. Add it.
Signed-off-by: NSimon Glass <sjg@chromium.org>

include/initcall.h

@@ -4,6 +4,11 @@
  * SPDX-License-Identifier:	GPL-2.0+
  */
 
+#ifndef __INITCALL_H
+#define __INITCALL_H
+
 typedef int (*init_fnc_t)(void);
 
 int initcall_run_list(const init_fnc_t init_sequence[]);
+
+#endif