iio: Add channel for Phase

Add new channel type support for phase.

This channel may be used by Time-of-flight sensors to express the
phase difference between emitted and received signals. Those sensor
will then use the phase shift of return signals to approximate the
distance to objects.

Signed-off-by: Mathieu Othacehe <m.othacehe@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

include/uapi/linux/iio/types.h

@@ -45,6 +45,7 @@ enum iio_chan_type {
 	IIO_INDEX,
 	IIO_GRAVITY,
 	IIO_POSITIONRELATIVE,
+	IIO_PHASE,
 };
 
 enum iio_modifier {