drm: rcar-du: dsi: Add 'select RESET_CONTROLLER'

The RCAR DSI driver uses reset controller, so we should select it in the
Kconfig.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>