drm/omap: venc: List both PAL and NTSC modes

The TV encoder supports both PAL and NTSC modes, but when queried for
the list of modes it supports, only the currently selected mode is
reported. Fix it and report the two modes unconditionally.

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>