remoteproc: wcss: add support for rpmsg communication

add glink and ssr subdevices for wcss rproc to enable rpmsg
communication.

Signed-off-by: Sivaprakash Murugesan <sivaprak@codeaurora.org>
Link: https://lore.kernel.org/r/1588350492-4663-1-git-send-email-sivaprak@codeaurora.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>