ARM: dts: sun9i: Add PRCM device node for the A80 dtsi

The PRCM is a collection of clock controls, reset controls, and various
power switches/gates. Some of these can be independently listed and
supported, while a number of CPU related ones are used in tandem with
CPUCFG for SMP bringup and CPU hotplugging.

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