Staging: iio: Documented output / DAC interface

Added documentation for:
* /sys/bus/iio/devices/deviceX/outY_scale
* /sys/bus/iio/devices/deviceX/outY_raw
* /sys/bus/iio/devices/deviceX/outY&Z_raw
Signed-off-by: NRoland Stigge <stigge@antcom.de>
Acked-by: NJonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/staging/iio/Documentation/sysfs-bus-iio

@@ -168,6 +168,7 @@ Description:
 What:		/sys/bus/iio/devices/deviceX/inY_scale
 What:		/sys/bus/iio/devices/deviceX/inY_supply_scale
 What:		/sys/bus/iio/devices/deviceX/in_scale
+What:		/sys/bus/iio/devices/deviceX/outY_scale
 What:		/sys/bus/iio/devices/deviceX/accel_scale
 What:		/sys/bus/iio/devices/deviceX/accel_peak_scale
 What:		/sys/bus/iio/devices/deviceX/gyro_scale
@@ -222,6 +223,23 @@ Description:
 		If a discrete set of scale values are available, they
 		are listed in this attribute.
 
+What:		/sys/bus/iio/devices/deviceX/outY_raw
+KernelVersion:	2.6.37
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Raw (unscaled, no bias etc.) output voltage for
+		channel Y.  The number must always be specified and
+		unique if the output corresponds to a single channel.
+
+What:		/sys/bus/iio/devices/deviceX/outY&Z_raw
+KernelVersion:	2.6.37
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Raw (unscaled, no bias etc.) output voltage for an aggregate of
+		channel Y, channel Z, etc.  This interface is available in cases
+		where a single output sets the value for multiple channels
+		simultaneously.
+
 What:		/sys/bus/iio/devices/deviceX/deviceX:eventY
 KernelVersion:	2.6.35
 Contact:	linux-iio@vger.kernel.org