uboot-imx

rockchip: rk3368: add Sheep board

Sheep board is designed by Rockchip as a EVB for rk3368.
Currently it is able to boot a linux kernel and system
to console with the miniloader run as fist level loader.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Andy Yan <andy.yan@rock-chips.com>