iio: light: vcnl4000: Add proximity ps_it for vcnl4200

Add ps_it attributes for vcnl4200 (similar to vcnl4040).
Add read/write attribute for proximity integration time.
Read attribute for available proximity integration times.
Change sampling rate depending on integration time.

Signed-off-by: Astrid Rost <astrid.rost@axis.com>
Link: https://lore.kernel.org/r/20230613135025.2596641-3-astrid.rost@axis.com


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