media: i2c: max96717: add test pattern ctrl

Add v4l2 test pattern control.

Signed-off-by: Tommaso Merciai <tomm.merciai@gmail.com>
Reviewed-by: Julien Massot <julien.massot@collabora.com>
Tested-by: Julien Massot <julien.massot@collabora.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>