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.
Signed-off-by: Marc Andre <marc.andre@netline.ch> Signed-off-by: Lars-Peter Clausen <lars@metafoo.de> Signed-off-by: Jonathan Cameron <jic23@kernel.org>