ARM: dts: add cubietech cubieboard4

Add a Cubietech Cubieboard4 device tree and instruct make to build it. This
device tree has been derived from the sun9i-a80-optimus.dts as they are very
similar in design[1]. Notably, I2C3 is not used on Cubieboard4 and the LED/PWM
definitions will need to be updated in the future.

[1] http://dl.cubieboard.org/model/cc-a80/Hardware/CC-A80-HW-V1.1.pdf

Signed-off-by: Tyler Baker <tyler.baker@linaro.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>