ARM: dtsi: axp81x: 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/axp81x.dtsi

@@ -48,6 +48,11 @@
 	interrupt-controller;
 	#interrupt-cells = <1>;
 
+	axp_adc: adc {
+		compatible = "x-powers,axp813-adc";
+		#io-channel-cells = <1>;
+	};
+
 	axp_gpio: axp-gpio {
 		compatible = "x-powers,axp813-gpio";
 		gpio-controller;