iio: ABI: add DAC 42kohm_to_gnd powerdown mode

Add a new powerdown mode for DACs with 42kohm resistor to GND.
Signed-off-by: Kim Seer Paller <kimseer.paller@analog.com>
Link: https://patch.msgid.link/20240718051834.32270-3-kimseer.paller@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/ABI/testing/sysfs-bus-iio

@@ -708,6 +708,7 @@ Description:
 		2.5kohm_to_gnd: connected to ground via a 2.5kOhm resistor,
 		6kohm_to_gnd: connected to ground via a 6kOhm resistor,
 		20kohm_to_gnd: connected to ground via a 20kOhm resistor,
+		42kohm_to_gnd: connected to ground via a 42kOhm resistor,
 		90kohm_to_gnd: connected to ground via a 90kOhm resistor,
 		100kohm_to_gnd: connected to ground via an 100kOhm resistor,
 		125kohm_to_gnd: connected to ground via an 125kOhm resistor,