dt-bindings: Add CPU hotplug cooling device

QTI CPU hotplug cooling devices.

The CPU hotplug cooling device will be used for hotpluging a CPU on a thermal

condition. This cooling device driver can register one cooling device per CPU,

which can be used by thermal zone to mitigate.

Each child node will represent a cooling device and the child node should

point to the CPU, which will be mitigated by that cooling device instance.

Properties:

- compatible:

	Usage: required

	Value type: <string>

	Definition: should be "qcom,cpu-hotplug"

Cooling device node:

- qcom,cpu:

	Usage: required

	Value type: <phandle>

	Definition: phandle to the CPU device that this cooling device will

			mitigate.

-#cooling-cells:

	Usage: required

	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,cpu-hotplug {

		compatible = "qcom,cpu-hotplug";

		cpu0_hotplug: cpu0-hotplug {

			qcom,cpu = <&CPU0>;

			#cooling-cells = <2>;

		};

		cpu1_hotplug: cpu1-hotplug {

			qcom,cpu = <&CPU1>;

			#cooling-cells = <2>;

		};

		cpu2_hotplug: cpu2-hotplug {

			qcom,cpu = <&CPU2>;

			#cooling-cells = <2>;

		};

		cpu3_hotplug: cpu3-hotplug {

			qcom,cpu = <&CPU3>;

			#cooling-cells = <2>;

		};

        };