dt-bindings: soc: qcom: Introduce Glink Pkt bindings

The RPMSG char driver requires clients to ioctl into a ctrl node to
create corresponding userspace char devices. Not all GLINK clients can
follow this standard. Add the GLINK PKT driver to create char devs from
boot time.

Change-Id: I363013b0cb99b8335b8d211ddd0116dfc95522ac