sh: Add asm/unaligned.h and asm/unaligned-sh4a.h from Linux kernel

zlib.c demands asm/unaligned.h. But, SH does not have these.
This commit add asm/unaligned.h and asm/unaligned-sh4a.h from Linux
kernel and modifyf for u-boot.

Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>