iio: ABI: Generalize ABI documentation for DAC

Introduces a more generalized ABI documentation for DAC. Instead of
having separate ABI files for each DAC, we now have a single ABI file
that covers the common sysfs interface for all DAC.

Signed-off-by: Kim Seer Paller <kimseer.paller@analog.com>
https://patch.msgid.link/20240718051834.32270-2-kimseer.paller@analog.com


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