ARM: dts: sun7i: Add A20-Marsboard

The Marsboard A20 is a A20 based SBC with 1G RAM, 8G Flash, micro SD
card slot , SATA socketm 10/100 ethernet, HDMI port, 4 USB2.0 ports, 2
USB2.0 OTG, USB WIFI(RTL8188EU) with antenna.

Signed-off-by: Conley Lee <conleylee@foxmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/tencent_C2E26D0935C9157CB3597BA4BD3316E8940A@qq.com