drm/omap: dsi: drop custom enable_te() API

Instead of using the custom enable_te() API, this automatically
enables/disables TE core support when a matching packet is sent
to the panel.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201215104657.802264-26-tomi.valkeinen@ti.com