ARM: dts: sun4i: A1000: add axp209 regulator nodes

This patch adds the regulator nodes for the axp209 by including
the axp209 dtsi.

DCDC2 is used as the cpu power supply. This patch also references
it from the cpu node.

Signed-off-by: Marcus Cooper <codekipper@gmail.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>