drm/omap: dsi: move enable/disable to bridge enable/disable

Clean up the code by inlining dsi_enable_video_outputs and
dsi_disable_video_outputs functions.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201215104657.802264-76-tomi.valkeinen@ti.com