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: I698cd90c508dcb94bc377b6c353deaead33d1b35
Signed-off-by: Chris Lew <clew@codeaurora.org>