drm: omapdrm: Move FEAT_DSI_* features to dsi driver

The FEAT_DSI_* features are specific to the DSI, move them from the
omap_dss_features structure to the dsi driver.

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