iio: adc: ad7625: add driver

iio: adc: ad7625: add driver

Add a driver for the AD762x and AD796x family of ADCs. These are
pin-compatible devices using an LVDS interface for data transfer,
capable of sampling at rates of 6 (AD7625), 10 (AD7626), and 5
(AD7960/AD7961) MSPS, respectively. They also feature multiple voltage
reference options based on the configuration of the EN1/EN0 pins, which
can be set in the devicetree.

Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>
Link: https://patch.msgid.link/20240909-ad7625_r1-v5-2-60a397768b25@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>