ARM: dts: sun7i: Add dts file for Wexler TAB7200

This patch add support for Wexler TAB7200 tablet.

The Wexler TAB7200 is a A20 based tablet with 7 inch display(800x480),
capacitive touchscreen(5 fingers), 1G RAM, 4G NAND, micro SD card slot,
mini HDMI port, 3.5mm audio plug, 1 USB OTG port and 1 USB 2.0 port.

Signed-off-by: Aleksei Mamlin <mamlinav@gmail.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>