ARM: dts: am335x-icev2: Add system-power-controller to RTC node

On the am335x-icev2 board [1], AM3359 PMIC_PWR_EN (ZCZ ball C6) is
connected to PWRHOLD (pin 1) on the TPS65910A3 PMIC. The addition of
system-power-controller to the rtc node will enable the capability of
the RTC driver to poweroff the board.

Based on commit 15c7be47fb7c ("ARM: dts: am335x: Add rtc node as
system-power-controller") by Keerthy in ti-linux-5.4.y branch [2].

[1] https://www.ti.com/tool/TMDSICE3359
[2] git://git.ti.com/ti-linux-kernel/ti-linux-kernel.git

Cc: Dave Gerlach <[e-mail]>
Cc: Keerthy <[e-mail]>
Link: https://lore.kernel.org/linux-omap/[e-mail]/
Suggested-by: Johan Hovold <[e-mail]>
Signed-off-by: Drew Fustini <[e-mail]>
Reviewed-by: Johan Hovold <[e-mail]>
Signed-off-by: Tony Lindgren <[e-mail]>

arch/arm/boot/dts/am335x-icev2.dts

···
 &pruss_tm {
 	status = "okay";
 };
+
+&rtc {
+	system-power-controller;
+};