arm: dts: am4372: setup rtc as system-power-controller

RTC alarm2 is connected to pmic_en line and hence can be used to control
the pmic enabling/disabling. Hence add the system-power-controller for rtc
node.

Signed-off-by: Keerthy <[e-mail]>
Signed-off-by: Tony Lindgren <[e-mail]>

arch/arm/boot/dts/am4372.dtsi

···
 			ti,hwmods = "rtc";
 			clocks = <&clk_32768_ck>;
 			clock-names = "int-clk";
+			system-power-controller;
 			status = "disabled";
 		};