ARM: dts: sun8i: tbs-a711: Add support for volume keys input

TBS A711 tablet has volume up/down keys connected to r_lradc. Add
support for these keys.
Signed-off-by: Ondrej Jirman <megous@megous.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>

arch/arm/boot/dts/sun8i-a83t-tbs-a711.dts

@@ -46,6 +46,7 @@
 
 #include <dt-bindings/gpio/gpio.h>
 #include <dt-bindings/pwm/pwm.h>
+#include <dt-bindings/input/input.h>
 
 / {
 	model = "TBS A711 Tablet";
@@ -219,6 +220,25 @@ &pwm {
 	status = "okay";
 };
 
+&r_lradc {
+	vref-supply = <&reg_aldo2>;
+	status = "okay";
+
+	button@210 {
+		label = "Volume Up";
+		linux,code = <KEY_VOLUMEUP>;
+		channel = <0>;
+		voltage = <210000>;
+	};
+
+	button@410 {
+		label = "Volume Down";
+		linux,code = <KEY_VOLUMEDOWN>;
+		channel = <0>;
+		voltage = <410000>;
+	};
+};
+
 &r_rsb {
 	status = "okay";