iio: proximity: vcnl3020: add periodic mode

Add the possibility to run proximity sensor in periodic measurement
mode with thresholds.

Reported-by: kernel test robot <lkp@intel.com> #repeated include
Signed-off-by: Ivan Mikhaylov <i.mikhaylov@yadro.com>
Link: https://lore.kernel.org/r/20210722154420.915082-3-i.mikhaylov@yadro.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>