rpmsg: glink: Add support for rpmsg glink chrdev

RPMSG provides a char device interface to userspace. Probe the rpmsg
chrdev channel to enable the rpmsg_ctrl device creation on glink
transports.

Signed-off-by: Chris Lew <clew@codeaurora.org>
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>
Signed-off-by: Deepak Kumar Singh <deesin@codeaurora.org>
Link: https://lore.kernel.org/r/1593017121-7953-4-git-send-email-deesin@codeaurora.org


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>