iio: Add channel for Position Relative

Add new channel type for relative position on a pad.

These type of analog sensor offers the position of a pen
on a touchpad, and is represented as a voltage, which can be
converted to a position on X and Y axis on the pad.
The channel will hand the relative position on the pad in both directions.

The channel can then be consumed by a touchscreen driver or
read as-is for a raw indication of the touchpen on a touchpad.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
diff --git a/tools/iio/iio_event_monitor.c b/tools/iio/iio_event_monitor.c
index b61245e..148f69d 100644
--- a/tools/iio/iio_event_monitor.c
+++ b/tools/iio/iio_event_monitor.c
@@ -58,6 +58,7 @@
 	[IIO_PH] = "ph",
 	[IIO_UVINDEX] = "uvindex",
 	[IIO_GRAVITY] = "gravity",
+	[IIO_POSITIONRELATIVE] = "positionrelative",
 };
 
 static const char * const iio_ev_type_text[] = {
@@ -151,6 +152,7 @@
 	case IIO_PH:
 	case IIO_UVINDEX:
 	case IIO_GRAVITY:
+	case IIO_POSITIONRELATIVE:
 		break;
 	default:
 		return false;