device property: Add FW type agnostic fwnode_graph_get_remote_node

Add fwnode_graph_get_remote_node() function which is equivalent to
of_graph_get_remote_node() on OF.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>