ARM: dts: sun5i: Add DT for HSG H702 tablet board

This is a Q8 format 7 inch tablet with an Allwinner A13 SoC.
It has 512MB DRAM, 4GB NAND flash, an accelerometer, camera,
RTL8188-based WiFi, and micro SD slot for external storage.

It is likely made by a subsidiary of Hanns.G (Hannstar).

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>