bindings: add support for qcom,pmic-glink

The PMIC Glink device provides the interface for clients to
communicate over GLink for sending/receiving data to/from
charger firmware that runs on a remote subsystem (e.g. ADSP)
which supports charging and gauging. Add the bindings for it.

Change-Id: Ia4f5ff346ebfa773bc0fe3d0410626ea67e1da31