uboot-imx

rockchip: add support for rk3288 PopMetal board

PopMetal is a rockchip rk3288 based board made by ChipSpark, which has
many interface such as HDMI, VGA, USB, micro-SD card, WiFi, Audio and
Gigabit Ethernet.

Signed-off-by: Ziyuan Xu <xzy.xu@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>