The NextThing Co. CHIP has an AXP209 PMIC and can be power-supplied by
ACIN via the CHG-IN pin.

This enables the ACIN power supply subnode in the DT.
Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>