bindings: Add altmode-glink

* QTI Type-C Alternate Mode over GLINK bindings

The Qualcomm Technologies, Inc. Type-C Alternate (alt) Mode GLINK device

provides an interface for Type-C alternate mode clients to receive data such as

Pin Assignment Notifications from the Type-C stack running on a remote

subsystem (e.g. DSP) via the PMIC GLINK interface.

Please refer to Documentation/devicetree/bindings/soc/qcom/qcom,pmic-glink.txt

for information on the "qcom,pmic_glink" device used in the example below.

REQUIRED PROPERTIES:

- compatible:

	Usage: required

	Value type: <stringlist>

	Definition: must be "qcom,altmode-glink"

- qcom,altmode-name:

	Usage: required

	Value type: <string>

	Definition: must be "altmode_N" where N is [0-9]

EXAMPLE:

&soc {

	qcom,pmic_glink {

		...

		qcom,altmode {

			compatible = "qcom,altmode-glink";

			qcom,altmode-name = "altmode_0";

		};

		...

	};

};