iio: light: vcnl4000: Add oversampling_ratio for 4040/4200

iio: light: vcnl4000: Add oversampling_ratio for 4040/4200

Add the proximity multi pulse (PS_MPS) as oversampling_ratio.
Instead of one single pulse per every defined time frame, one can
program2, 4, or even 8 pulses. This leads to a longer IRED on-time
for each proximity measurement value, which also results in a higher
detection range.

Add read/write attribute for proximity oversampling-ratio and read
attribute for available oversampling-ratio.
This is supported for vcnl4040 and vcnl4200.

Signed-off-by: Astrid Rost <astrid.rost@axis.com>
Link: https://lore.kernel.org/r/20230613135025.2596641-8-astrid.rost@axis.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>