Documentation: ABI: IIO: Re-add sysfs-bus-iio-adc-ad4130

Documentation: ABI: IIO: Re-add sysfs-bus-iio-adc-ad4130

The ad4130 driver exports in_voltageY-voltageZ_filter_mode and
in_voltage-voltage_filter_mode_available attributes to user space. A
previous patch merged the documentation for those attributes with the
documentation for filter_type/filter_type_available into sysfs-bus-iio.
Filter mode and filter type refer to the same feature which is the digital
filter applied over ADC samples. However, since datasheets use the term
`filter type` and ad4130 driver is the only one using filter_mode,
deprecate the filter_mode ABI in favor of filter_type and keep the docs
separate to avoid confusion and intricate attribute descriptions.

Fixes: 01bb12922b60 ("Documentation: ABI: added filter mode doc in sysfs-bus-iio")
Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/c77b2d65f1115c1c394582f55944d6f685058f9c.1738680728.git.marcelo.schmitt@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>