iio: adc: ad4851: add ad485x driver

Add support for the AD485X a fully buffered, 8-channel simultaneous
sampling, 16/20-bit, 1 MSPS data acquisition system (DAS) with
differential, wide common-mode range inputs.

Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Link: https://patch.msgid.link/20250214131955.31973-10-antoniu.miclaus@analog.com


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