ARM: dtsi: axp209: add node for ADC

This adds a DT node for the ADC of the PMIC so that there can be
consumers of its IIO channels declaring their consumptions via DT.
Signed-off-by: Quentin Schulz <quentin.schulz@bootlin.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>

arch/arm/boot/dts/axp209.dtsi

@@ -58,6 +58,11 @@ ac_power_supply: ac-power-supply {
 		status = "disabled";
 	};
 
+	axp_adc: adc {
+		compatible = "x-powers,axp209-adc";
+		#io-channel-cells = <1>;
+	};
+
 	axp_gpio: gpio {
 		compatible = "x-powers,axp209-gpio";
 		gpio-controller;