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 <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Heiko Stuebner <[e-mail]>

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

···
  */
 
 /dts-v1/;
+#include <dt-bindings/input/input.h>
 #include "rk3066a.dtsi"
 
 / {
···
 	memory@60000000 {
 		reg = <0x60000000 0x40000000>;
 		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 {
···
 				remote-endpoint = <&hdmi_out_con>;
 			};
 		};
+	};
+
+	vcc_2v5: vcc-2v5 {
+		compatible = "regulator-fixed";
+		regulator-name = "vcc_2v5";
+		regulator-min-microvolt = <2500000>;
+		regulator-max-microvolt = <2500000>;
 	};
 
 	vcc_io: vcc-io {
···
 			rockchip,pins = <3 RK_PD0 RK_FUNC_GPIO &pcfg_pull_none>;
 		};
 	};
+};
+
+&saradc {
+	vref-supply = <&vcc_2v5>;
+	status = "okay";
 };
 
 &uart2 {