ARM: dtsi: axp81x: set pinmux for GPIO0/1 when used as LDOs

On AXP813/818, GPIO0 and GPIO1 can be used as LDO as (respectively)
ldo_io0 and ldo_io1.

Let's add the pinctrl properties to the said regulators.

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