Userspace cooling devices.

Certain Cooling devices reside in userspace and they also needs to be
mitigated for thermal conditions. Thermal framework will send netlink message
to userspace, when a cooling device level changes for any cooling device.
This cooling device expects the userspace cooling device to listen to the
netlink message and take necessary action.

Devicetree will define the name of the cooling device and the max mitigation
level a cooling device can support. Each child node will be an individual
cooling device.

Properties:

- compatible:
	Usage: required
	Value type: <string>
	Definition: should be "qcom,userspace-cooling-devices"


Subsystem properties:
	Minimum one child node is required. Child node name is used as
	cooling device name and phandle for that cooling device.

	Cooling device node properties:
	-qcom,max-level:
		Usage: required
		Value type: <integer>
		Definition: The max level this cooling device can support.
			The cooling device levels start from 0 to max level
			inclusive.

	-#cooling-cells:
		Usage: optional
		Value type: <integer>
		Definition: Must be 2. Needed for of_thermal as cooling device
			identifier. Please refer to
			<devicetree/bindings/thermal/thermal.txt> for more
			details.
Example:

	qcom,userspace-cdev {
		compatible = "qcom,userspace-cooling-devices";

		display_fps: display-fps {
			qcom,max-level = <4>;
			/*levels supported
			* 0, 1, 2, 3, 4
			*/
			#cooling-cells = <2>;
		};
	};