ARM: dts: add rk3288 PopMetal board

PopMetal is a rockchip rk3288 based board made by ChipSpark,
which has many interface such as VGA,HDMI,usb,ir,sdcad and lots of
sensors such as gyroscope(L3G4200D),accelerometer(mma8452),
compass(AK8963C).

This patch add a basic support for this board, which make the board
boot into a initramfs shell with sdcard,hdmi and all sensors enabled
Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>