drm: omapdrm: Move FEAT_* features to dispc driver

All the remaining FEAT_* features are specific to the DISPC, move them
from the omap_dss_features structure to the dispc driver.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>