ARM: dts: sun8i: Add basic dtsi file for Allwinner R40

The Allwinner R40 SoC is marketed as the successor to the A20 SoC.
The R40 is a smaller chip than the A20, but features the same set
of programmable pins, with a couple extra pins and some new pin
functions. The chip features 4 Cortex-A7 cores and a Mali-400 MP2
GPU. It retains most if not all features from the A20, while adding
some new features, such as MIPI DSI output, or updating various
hardware blocks, such as DE 2.0.

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