iio: light: apds9960: Add proximity and gesture offset calibration

Proximity and gesture offset registers perform offset correction to
improve cross-talk performance. Added `calibbias` to the proximity
and gesture channels.
Provided facility to set calibbias based on the channel number.

Signed-off-by: Abhash Jha <abhashkumarjha123@gmail.com>
Link: https://patch.msgid.link/20240804134212.51682-2-abhashkumarjha123@gmail.com


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