dt-bindings: iio: adf4371: add refin mode

Add support for selecting between single-ended and differential
reference input.

Input frequency boundaries are change based on the mode selected
(single-ended/differential).

Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20250127101026.5320-2-antoniu.miclaus@analog.com


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