board_f: initcall: Add a header guard

This file is missing the usual header guard. Add it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/initcall.h b/include/initcall.h
index 65f67dc..fe7e903 100644
--- a/include/initcall.h
+++ b/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