ARM: dts: add device tree for Gemini SoC and SQ201

This adds a device tree for the Gemini SoC and the ITian
Square One SQ201 board that has been my testing target
for Gemini device tree support.

Cc: Janos Laube <janos.dev@gmail.com>
Cc: Paulius Zaleckas <paulius.zaleckas@gmail.com>
Cc: Hans Ulli Kroll <ulli.kroll@googlemail.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>