iio:ad5064: Add support for ltc2617 and similar devices

The Linear Technology LTC2606, LTC2607, LTC2609, LTC2616, LTC2617,
LTC2619, LTC2626, LTC2627 and LTC2629 devices are very similar
to the AD5064 device.

This patch adds support for those devices.

Datasheet for LTC devices:
LTC2606, LTC2616, LTC2626: http://www.linear.com/docs/6398
LTC2607, LTC2617, LTC2627: http://www.linear.com/docs/8977
LTC2709, LTC2619, LTC2629: http://www.linear.com/docs/8477

Signed-off-by: Marc Andre <[email protected]>
Signed-off-by: Lars-Peter Clausen <[email protected]>
Signed-off-by: Jonathan Cameron <[email protected]>
diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
index 80c6fce..3c66248 100644
--- a/Documentation/ABI/testing/sysfs-bus-iio
+++ b/Documentation/ABI/testing/sysfs-bus-iio
@@ -496,6 +496,7 @@
 		1kohm_to_gnd: connected to ground via an 1kOhm resistor,
 		6kohm_to_gnd: connected to ground via a 6kOhm resistor,
 		20kohm_to_gnd: connected to ground via a 20kOhm 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,
 		500kohm_to_gnd: connected to ground via a 500kOhm resistor,