board: amlogic: jethub j100: enable saradc in dts

Prepare to use ADC channel 1 to check the hardware revision of the board:
- add u-boot dts include with saradc node

Signed-off-by: Vyacheslav Bocharov <adeep@lexina.in>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20220424082159.757622-6-adeep@lexina.in

arch/arm/dts/meson-axg-jethome-jethub-j100-u-boot.dtsi

@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: (GPL-2.0+ OR MIT)
+/*
+ * Copyright (c) 2022 Vyacheslav Bocharov <adeep@lexina.in>
+ * Author: Vyacheslav Bocharov <adeep@lexina.in>
+ */
+
+&saradc {
+	status = "okay";
+	vref-supply = <&vddio_ao18>;
+};