arm64: dts: rockchip: make poweroff(8) work on Radxa ROCK 5A

Designate the RK806 PMIC on the Radxa ROCK 5A as the system power
controller, so the board shuts down properly on poweroff(8).

Fixes: 75fdcbc ("arm64: dts: rockchip: add PMIC to rock-5a")
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Signed-off-by: FUKAUMI Naoki <naoki@radxa.com>
Link: https://lore.kernel.org/r/20240612033523.37166-1-naoki@radxa.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

Author: RadxaNaoki

arch/arm64/boot/dts/rockchip/rk3588s-rock-5a.dts

@@ -394,6 +394,7 @@
 		pinctrl-0 = <&pmic_pins>, <&rk806_dvs1_null>,
 			    <&rk806_dvs2_null>, <&rk806_dvs3_null>;
 		spi-max-frequency = <1000000>;
+		system-power-controller;
 
 		vcc1-supply = <&vcc5v0_sys>;
 		vcc2-supply = <&vcc5v0_sys>;