ARM: dts: sun7i: bananapi-m1-plus: Add PMIC regulators

The Bananapi M1+, like other Allwinner A20 based boards, uses the
AXP209 PMIC to supply its power.

Add the AXP209 regulators.

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