sunxi: Split out common board design for ALL-H3-CC device tree

The Libre Computer Project ALL-H3-CC has three models, all using the
same board design, but with different pin compatible SoCs and amount of
DRAM.

Currently only the H3 1GB DRAM variant is supported. To support the two
other variants, first split the original device tree into a common board
design part and an SoC specific part.

The SoC part only defines which SoC is used and model name, and includes
the SoC specific dtsi file and the common design dtsi file.

Also fix up the SPDX identifier line to use the correct comment style,
and place it on the first line.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>