ARM: dts: rockchip: add dts for RK3288-Fennec boards

This adds support for RK3288-Fennec boards. Currently supported
are serial console, wired networking, hdmi output and USB.

Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>