media: v4l2-core: Make the v4l2-core code enable/disable the privacy LED if present

Make v4l2_async_register_subdev_sensor() try to get a privacy LED
associated with the sensor and extend the call_s_stream() wrapper to
enable/disable the privacy LED if found.

This makes the core handle privacy LED control, rather then having to
duplicate this code in all the sensor drivers.

Suggested-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Link: https://lore.kernel.org/r/20230127203729.10205-2-hdegoede@redhat.com