ARM: dts: rockchip: add adc-keys node to rk3066a-mk808

The MK808 has a button inside the cover for the boot loader to do
some action. Add the adc-keys node to the rk3066a-mk808.dts file.
The rk3066 has a higher maximum DC supply voltage for the analog part of
SAR-ADC VDDA_SARADC of 2.75V then other Rockchip SoCs.
For the "rockchip,saradc" node is a vref-supply property required,
so add a regulator for it as well.
Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Link: https://lore.kernel.org/r/20210828092755.24560-1-jbx6244@gmail.comSigned-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm/boot/dts/rk3066a-mk808.dts

@@ -4,6 +4,7 @@
  */
 
 /dts-v1/;
+#include <dt-bindings/input/input.h>
 #include "rk3066a.dtsi"
 
 / {
@@ -24,6 +25,20 @@ memory@60000000 {
 		device_type = "memory";
 	};
 
+	adc-keys {
+		compatible = "adc-keys";
+		io-channels = <&saradc 1>;
+		io-channel-names = "buttons";
+		keyup-threshold-microvolt = <2500000>;
+		poll-interval = <100>;
+
+		recovery {
+			label = "recovery";
+			linux,code = <KEY_VENDOR>;
+			press-threshold-microvolt = <0>;
+		};
+	};
+
 	gpio-leds {
 		compatible = "gpio-leds";
 
@@ -46,6 +61,13 @@ hdmi_con_in: endpoint {
 		};
 	};
 
+	vcc_2v5: vcc-2v5 {
+		compatible = "regulator-fixed";
+		regulator-name = "vcc_2v5";
+		regulator-min-microvolt = <2500000>;
+		regulator-max-microvolt = <2500000>;
+	};
+
 	vcc_io: vcc-io {
 		compatible = "regulator-fixed";
 		regulator-name = "vcc_io";
@@ -164,6 +186,11 @@ wifi_pwr: wifi-pwr {
 	};
 };
 
+&saradc {
+	vref-supply = <&vcc_2v5>;
+	status = "okay";
+};
+
 &uart2 {
 	status = "okay";
 };