iio: light: vcnl4000: Add calibration bias for 4040/4200

The calibration bias is setting the LED current to change the detection
distance. Add read/write attribute for proximity calibration bias and
read attribute for available values. This is supported for vcnl4040 and
vcnl4200.

Signed-off-by: Astrid Rost <astrid.rost@axis.com>
Link: https://lore.kernel.org/r/20230613135025.2596641-9-astrid.rost@axis.com


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