drm/omap: Add a dss device operation flag for .get_modes()

Instead of manually iterating over the dss devices in the pipeline to
find the first one that implements the .get_modes() operation, add a new
operation flag for .get_modes() and use the omap_connector_find_device()
helper function to locate the right dss device.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Tested-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/gpu/drm/omapdrm/displays/panel-tpo-td043mtea1.c

@@ -422,6 +422,7 @@ static int tpo_td043_probe(struct spi_device *spi)
 	dssdev->type = OMAP_DISPLAY_TYPE_DPI;
 	dssdev->owner = THIS_MODULE;
 	dssdev->of_ports = BIT(0);
+	dssdev->ops_flags = OMAP_DSS_DEVICE_OP_MODES;
 
 	/*
 	 * Note: According to the panel documentation: