rpmsg: glink: Introduce glink smem based transport

The glink protocol supports different types of transports (shared
memory). With the core protocol remaining the same, the way the
transport's memory is probed and accessed is different. So add support
for glink's smem based transports.

Adding a new smem transport register function and the fifo accessors for
the same.

Acked-by: Arun Kumar Neelakantam <aneela@codeaurora.org>
Signed-off-by: Sricharan R <sricharan@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/rpmsg/qcom_glink_native.c

@@ -1010,3 +1010,8 @@ void qcom_glink_native_remove(struct qcom_glink *glink)
 	idr_destroy(&glink->rcids);
 	mbox_free_channel(glink->mbox_chan);
 }
+
+void qcom_glink_native_unregister(struct qcom_glink *glink)
+{
+	device_unregister(glink->dev);
+}