iio: amplifiers: ad8366: add support for adrf5702/3 Add chip info structs and device table entries for ADRF5702 and ADRF5703 Digital Step Attenuators. Reviewed-by: Nuno Sá <nuno.sa@analog.com> Signed-off-by: Rodrigo Alencar <rodrigo.alencar@analog.com> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>