The axp209.dtsi defines nodes for ac, usb and battery supplies for a
while now. This patch enables these nodes for the A20-Olinuxino-Micro,
which has connectors for all three of them.

The patch was run-tested against linux-next-20170825.
Signed-off-by: Harald Geyer <harald@ccbib.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>