drm/omap: omap_display_timings: Use display_flags for interlace mode

Remove the interlace member and add display_flags to omap_video_timings to
configure the interlace mode.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>