iio: Added ABI description for quaternion

Added documentation for reading quaternion components for 3D rotations.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/ABI/testing/sysfs-bus-iio

@@ -792,6 +792,7 @@ What:		/sys/.../iio:deviceX/scan_elements/in_incli_x_en
 What:		/sys/.../iio:deviceX/scan_elements/in_incli_y_en
 What:		/sys/.../iio:deviceX/scan_elements/in_pressureY_en
 What:		/sys/.../iio:deviceX/scan_elements/in_pressure_en
+What:		/sys/.../iio:deviceX/scan_elements/in_rot_quaternion_en
 KernelVersion:	2.6.37
 Contact:	linux-iio@vger.kernel.org
 Description:
@@ -807,6 +808,7 @@ What:		/sys/.../iio:deviceX/scan_elements/in_voltageY_supply_type
 What:		/sys/.../iio:deviceX/scan_elements/in_timestamp_type
 What:		/sys/.../iio:deviceX/scan_elements/in_pressureY_type
 What:		/sys/.../iio:deviceX/scan_elements/in_pressure_type
+What:		/sys/.../iio:deviceX/scan_elements/in_rot_quaternion_type
 KernelVersion:	2.6.37
 Contact:	linux-iio@vger.kernel.org
 Description:
@@ -853,6 +855,7 @@ What:		/sys/.../iio:deviceX/scan_elements/in_incli_y_index
 What:		/sys/.../iio:deviceX/scan_elements/in_timestamp_index
 What:		/sys/.../iio:deviceX/scan_elements/in_pressureY_index
 What:		/sys/.../iio:deviceX/scan_elements/in_pressure_index
+What:		/sys/.../iio:deviceX/scan_elements/in_rot_quaternion_index
 KernelVersion:	2.6.37
 Contact:	linux-iio@vger.kernel.org
 Description:
@@ -899,3 +902,12 @@ Contact:	linux-iio@vger.kernel.org
 Description:
 		This attribute is used to get/set the integration time in
 		seconds.
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_rot_quaternion_raw
+KernelVersion:	3.15
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Raw value of quaternion components using a format
+		x y z w. Here x, y, and z component represents the axis about
+		which a rotation will occur and w component represents the
+		amount of rotation.