Add missing *BSD copyright headers.

	* include/grub/aout.h: Add BSD licence.
	* include/grub/i386/bsd.h: Parts under different licences moved to ...
	* include/grub/i386/freebsd_linker.h: ... here,
	* include/grub/i386/freebsd_reboot.h: ... here,
	* include/grub/i386/netbsd_bootinfo.h: ... here,
	* include/grub/i386/netbsd_reboot.h: ... here,
	* include/grub/i386/openbsd_bootarg.h: ... here,
	* include/grub/i386/openbsd_reboot.h: ... and here. Added appropriate
	licence to each file.