board_f: Make relocation functions generic

This header file is used by three archs. It could be used by all of them
since relocation is a common function. Move it into a generic file.

Signed-off-by: Simon Glass <sjg@chromium.org>

arch/xtensa/include/asm/relocate.h

@@ -1,14 +0,0 @@
-/*
- * Copyright (C) 2016 Cadence Design Systems Inc.
- *
- * SPDX-License-Identifier:	GPL-2.0+
- */
-
-#ifndef _ASM_XTENSA_RELOCATE_H
-#define _ASM_XTENSA_RELOCATE_H
-
-#include <common.h>
-
-int clear_bss(void);
-
-#endif	/* _ASM_XTENSA_RELOCATE_H */