media: Documentation: kapi: Add v4l2 generic ISP support

media: Documentation: kapi: Add v4l2 generic ISP support

Add to the driver-api documentation the v4l2-isp.h types and
helpers documentation.

Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
Reviewed-by: Michael Riesch <michael.riesch@collabora.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>