ARM: dts: sun9i: Add CPUCFG device node for A80 dtsi

CPUCFG is a collection of registers that are mapped to the SoC's signals
from each individual processor core and associated peripherals, such as
resets for processors, L1/L2 cache and other things.

These registers are used for SMP bringup and CPU hotplugging.

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