linux/Documentation/devicetree/bindings/power/power-controller.txt

* Generic system power control capability

Power-management integrated circuits or miscellaneous hardware components are
sometimes able to control the system power. The device driver associated with these
components might need to define this capability, which tells the kernel that
it can be used to switch off the system. The corresponding device must have the
standard property "system-power-controller" in its device node. This property
marks the device as able to control the system power. In order to test if this
property is found programmatically, use the helper function
"of_device_is_system_power_controller" from of.h .

Example:

act8846: act8846@5 {
	 compatible = "active-semi,act8846";
	 status = "okay";
	 system-power-controller;
}