iio: pressure: bmp280: Add more tunable config parameters for BMP380

Allows sampling frequency and IIR filter coefficients configuration
using sysfs ABI.

The IIR filter coefficient is configurable using the sysfs attribute
"filter_low_pass_3db_frequency".

Signed-off-by: Angel Iglesias <ang.iglesiasg@gmail.com>
Link: https://lore.kernel.org/r/876f8a2277f71672488e99aa02aae4239d530f51.1663025017.git.ang.iglesiasg@gmail.com


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