rpmsg: Introduce a driver override mechanism

Similar to other subsystems it's useful to provide a mechanism to force
a specific driver match on a device, so introduce this.

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

drivers/rpmsg/rpmsg_core.c

@@ -315,6 +315,9 @@ static int rpmsg_dev_match(struct device *dev, struct device_driver *drv)
 	const struct rpmsg_device_id *ids = rpdrv->id_table;
 	unsigned int i;
 
+	if (rpdev->driver_override)
+		return !strcmp(rpdev->driver_override, drv->name);
+
 	if (ids)
 		for (i = 0; ids[i].name[0]; i++)
 			if (rpmsg_id_match(rpdev, &ids[i]))