ARM64: dts: meson-axg: add s400 main 12v supply

Add a fixed regulator for the main 12v which is the main power supply
of the board.
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

arch/arm64/boot/dts/amlogic/meson-axg-s400.dts

@@ -16,6 +16,13 @@ aliases {
 		serial1 = &uart_A;
 	};
 
+	main_12v: regulator-main_12v {
+		compatible = "regulator-fixed";
+		regulator-name = "12V";
+		regulator-min-microvolt = <12000000>;
+		regulator-max-microvolt = <12000000>;
+	};
+
 	vddio_boot: regulator-vddio_boot {
 		compatible = "regulator-fixed";
 		regulator-name = "VDDIO_BOOT";