ARM: dts: sunxi: Add regulators for Sinovoip BPI-M2

Add the needed node for DFVS on Sinovoip BPI-M2.
This add the axp221 under the p2wi node, the regulators and
the cpu-supply property for cpu0.

Signed-off-by: Emmanuel Vadot <manu@bidouilliste.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>