soc: qcom: glink_pkt: Refactor to use rpmsg

Change the glink_pkt driver to use the rpmsg interface instead of
directly using glink. This change bridges dynamic rpmsg devices to
static device nodes for userspace to use.

Change-Id: I8c5f25f38facf32c5259bf8558e3392b9bd80e8d
Signed-off-by: Chris Lew <clew@codeaurora.org>