ARM: dts: rockchip: add system-power-controller to act8846 on radxarock

The act8846 is the main pmic and system-power-controller on radxarock boards,
so add the necessary property.
Signed-off-by: Michael Niewoehner <mniewoeh@stud.hs-offenburg.de>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm/boot/dts/rk3188-radxarock.dts

@@ -152,6 +152,7 @@ act8846: act8846@5a {
 		compatible = "active-semi,act8846";
 		reg = <0x5a>;
 		status = "okay";
+		system-power-controller;
 
 		pinctrl-names = "default";
 		pinctrl-0 = <&act8846_dvs0_ctl>;