dt-bindings: power: supply: add AXP20X/AXP22X AC power supply

AXP20X and AXP22X PMICs' AC power supply

Required Properties:

 - compatible: One of:

			"x-powers,axp202-ac-power-supply"

			"x-powers,axp221-ac-power-supply"

This node is a subnode of the axp20x PMIC.

The AXP20X can read the current current and voltage supplied by AC by

reading ADC channels from the AXP20X ADC.

The AXP22X is only able to tell if an AC power supply is present and

usable.

Example:

&axp209 {

	ac_power_supply: ac-power-supply {

		compatible = "x-powers,axp202-ac-power-supply";

	};

};