bootm: Adjust arguments of boot_os_fn

bootm: Adjust arguments of boot_os_fn

Adjust boot_os_fn to use struct bootm_info instead of the separate
argc, argv and image parameters. Update the handlers accordingly. Few
of the functions make use of the arguments, so this improves code size
slightly.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>