dt-bindings: thermal: Add AOP regulator cooling device bindings

RPMh regulator cooling device.

The RPMh regulator cooling device, will be used to place a voltage floor

restriction on a rail. This cooling device will use a QMP AOP mail box to send

the message to apply and clear voltage floor restriction.

The cooling device node should be a child of the regulator devicetree node,

which it is trying to place the floor restriction.

Properties:

- compatible:

	Usage: required

	Value type: <string>

	Definition: shall be "qcom,rpmh-reg-cdev"

- qcom,reg-resource-name:

	Usage: required

	Value type: <string>

	Definition: The regulator resource name to be used for communicating

			with RPMh. This value should be any of the below

			resource name,

			cx -> For CX rail,

			mx -> For MX rail,

			ebi -> For EBI rail.

- mboxes:

	Usage: required

	Value type: <phandle>

	Definition: A phandle to the QMP AOP mail box, that needs to be used

			for sending the floor restriction message.

- #cooling-cells: Must be 2. Please refer to

			<devicetree/bindings/thermal/thermal.txt> for more

			details.

Example:

	vdd_cx: rpmh-cx-regulator-cdev {

		compatible = "qcom,rpmh-reg-cdev";

		mboxes = <&qmp_aop 0>;

		qcom,reg-resource-name = "cx";

		#cooling-cells = <2>;

	};