ARM: sun5i: chip: enable battery power supply subnode

The NextThing Co. CHIP has an AXP209 PMIC with battery connector.

This enables the battery power supply subnode.

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