ARM: sun6i: a31: hummingbird: Enable AXP221's ACIN power supply

The ACIN pins of the AXP221 PMIC on the A31 Hummingbird are tied to the
DC jack on the board through a 12V to 5V buck converter.

Enable the ACIN power supply.

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