device property: Add fwnode_graph_get_port_parent

Provide a helper to obtain the parent device fwnode without first
parsing the remote-endpoint as per fwnode_graph_get_remote_port_parent.

Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
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>