ARM: dts: sunxi: add support for Orange Pi Zero board

Orange Pi Zero is a board that came with the new Allwinner H2+ SoC and a
SDIO Wi-Fi chip by Allwinner (XR819).

Add a device tree file for it.

Signed-off-by: Icenowy Zheng <icenowy@aosc.xyz>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>