arm64: dts: rockchip: Add maskrom button to NanoPi R5S + R5C

Both the R5S and R5C have a MASKROM button connected via saradc.
For both the R5S as the R5C it's described on page 9 of their
respective schematic, identified as 'Recovery'.

Signed-off-by: Diederik de Haas <didi.debian@cknow.org>
Link: https://lore.kernel.org/r/20250716083355.327451-1-didi.debian@cknow.org
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

Author: diederikdehaas

arch/arm64/boot/dts/rockchip/rk3568-nanopi-r5s.dtsi

@@ -25,6 +25,20 @@
 		stdout-path = "serial2:1500000n8";
 	};
 
+	adc-keys {
+		compatible = "adc-keys";
+		io-channels = <&saradc 0>;
+		io-channel-names = "buttons";
+		keyup-threshold-microvolt = <1800000>;
+		poll-interval = <100>;
+
+		button-maskrom {
+			label = "MASKROM";
+			linux,code = <KEY_SETUP>;
+			press-threshold-microvolt = <0>;
+		};
+	};
+
 	hdmi-con {
 		compatible = "hdmi-connector";
 		type = "a";