rockchip: rk3308: Add support for ROC-RK3308-CC board

ROC-RK3308-CC is a rk3308 based board designed by
Firelfy, with eMMC and 256MB DDR3 and RTL8188 Wifi
on board.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>