uboot-imx

sandbox: allow processing before main loop

In order to pass command line arguments to sandbox we need to be able
to act on them. So take control back at the end of board_init_r() from
where we can call the main loop or do something else.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>