media: v4l2-subdev: Limit the number of active routes to V4L2_FRAME_DESC_ENTRY_MAX

media: v4l2-subdev: Limit the number of active routes to V4L2_FRAME_DESC_ENTRY_MAX

Drivers that implement routing need to report a frame descriptor
accordingly, with up to one entry per route. The number of frame
descriptor entries is fixed to V4L2_FRAME_DESC_ENTRY_MAX, currently
equal to 8. Multiple drivers therefore limit the number of routes to
V4L2_FRAME_DESC_ENTRY_MAX, with a note indicating that the limit should
be lifted when frame descriptor entries will be allocated dynamically.

Duplicating the check in multiple drivers isn't ideal. Move it to the
VIDIOC_SUBDEV_S_ROUTING handling code in the v4l2-subdev core.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>