ARM: dts: sun4i: Add AXP209 PMU regulators for pcDuino1/2

This allows voltage-scaling with cpufreq-dt. The reliability of
voltage-scaling has been checked by reducing the voltage of all
operating points by 0.025V (for extra safety headroom) and running
libjpeg-turbo decoding tests on 5 pcDuino2 boards. It means that
the standard sun4i voltages should be perfectly fine too.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>