rockchip: Add support for MiQi rk3288 board

MiQi is rk3288 based development board with 1 or 2 GB SDRAM, 16 GB eMMC,
micro SD card interface, 4 USB 2.0 ports, HDMI, gigabit Ethernet and
expansion ports.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Eddie Cai <eddie.cai.linux@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>