Unlike the other AD719Xs, AD7194 has configurable channels. The user can
dynamically configure them in the devicetree.

Also add an example for AD7194 devicetree.
Signed-off-by: Alisa-Dariana Roman <alisa.roman@analog.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240514120222.56488-6-alisa.roman@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>