iio: adc: ad7173: add openwire detection support for single conversions

Some chips of the ad7173 family supports open wire detection.

Generate a level fault event whenever an external source is disconnected
from the system input on single conversions.

Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Signed-off-by: Guillaume Ranquet <granquet@baylibre.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20250127-ad4111_openwire-v5-2-ef2db05c384f@baylibre.com


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