docs: iio: add documentation for adis16480 driver

Add documentation for adis16480 driver which describes the driver
device files and shows how the user may use the ABI for various
scenarios (configuration, measurement, etc.).

Signed-off-by: Ramona Gradinariu <ramona.gradinariu@analog.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20240528142409.239187-7-ramona.gradinariu@analog.com


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