arm64: dts: rockchip: Add 12V DCIN regulator to rk3399-ficus

12V DCIN regulator is root source supply for the rest of regulators
in Rock960 power diagram.

Add support for it and attach same to supply vcc5v0_sys.
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Akash Gajjar <akash@openedev.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm64/boot/dts/rockchip/rk3399-rock960.dtsi

@@ -18,6 +18,15 @@ sdio_pwrseq: sdio-pwrseq {
 		reset-gpios = <&gpio0 RK_PB2 GPIO_ACTIVE_LOW>;
 	};
 
+	vcc12v_dcin: vcc12v-dcin {
+		compatible = "regulator-fixed";
+		regulator-name = "vcc12v_dcin";
+		regulator-min-microvolt = <12000000>;
+		regulator-max-microvolt = <12000000>;
+		regulator-always-on;
+		regulator-boot-on;
+	};
+
 	vcc1v8_s0: vcc1v8-s0 {
 		compatible = "regulator-fixed";
 		regulator-name = "vcc1v8_s0";
@@ -32,6 +41,7 @@ vcc5v0_sys: vcc5v0-sys {
 		regulator-min-microvolt = <5000000>;
 		regulator-max-microvolt = <5000000>;
 		regulator-always-on;
+		vin-supply = <&vcc12v_dcin>;
 	};
 
 	vcc3v3_sys: vcc3v3-sys {