ARM: sun7i: a20: bananapi-m1-plus: Enable AXP209's ACIN power supply

The ACIN pins of the AXP209 PMIC on the Bananapi M1 Plus are tied to the
"power input" micro USB connector next to the SATA connector on the board.

Enable the ACIN power supply.

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