ARM64: dts: meson-gxl-libretech-cc: enable saradc

Enable saradc and add the reference 1.8v regulator required.
The libretech-cc has saradc channel 0 and 2 available on the 2 first
pins of 2J3 header
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

arch/arm64/boot/dts/amlogic/meson-gxl-s905x-libretech-cc.dts

@@ -96,6 +96,13 @@ vcc_card: regulator-vcc-card {
 		regulator-settling-time-down-us = <50000>;
 	};
 
+	vddio_ao18: regulator-vddio_ao18 {
+		compatible = "regulator-fixed";
+		regulator-name = "VDDIO_AO18";
+		regulator-min-microvolt = <1800000>;
+		regulator-max-microvolt = <1800000>;
+	};
+
 	vddio_boot: regulator-vddio_boot {
 		compatible = "regulator-fixed";
 		regulator-name = "VDDIO_BOOT";
@@ -196,6 +203,11 @@ &pinctrl_periphs {
 			  "7J1 Header Pin15";
 };
 
+&saradc {
+	status = "okay";
+	vref-supply = <&vddio_ao18>;
+};
+
 /* SD card */
 &sd_emmc_b {
 	status = "okay";