iio: light: tcs3472: support out-of-threshold events

The TCS3472 device provides interrupt signal for out-of-threshold events
with persistence filter.

This change adds interrupt support for the threshold events and enables
to configure the period of time by persistence filter.

Cc: Peter Meerwald <pmeerw@pmeerw.net>
Cc: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>