drm/omap: dsi: fix DCS_CMD_ENABLE

We only need to set VC_CTRL:DCS_CMD_ENABLE for command mode panels when
the HW has DSI_QUIRK_DCS_CMD_CONFIG_VC quirk. The old code did this
right by accident, but now we set DCS_CMD_ENABLE for video mode panels
too.

Fix this by skipping the set for video mode.

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/20201215104657.802264-84-tomi.valkeinen@ti.com