ARM: dts: sun8i: sina33: enable battery power supply subnode

The Sinlinx SinA33 has an AXP223 PMIC and a battery connector, thus, we
enable the battery power supply subnode in its Device Tree.

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>