dt-binding: ptp_qoriq: add little-endian support

Specify "little-endian" property if the 1588 timer IP block
is little-endian mode. The default endian mode is big-endian.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/ptp/ptp-qoriq.txt

@@ -19,6 +19,9 @@ Clock Properties:
   - fsl,max-adj      Maximum frequency adjustment in parts per billion.
   - fsl,extts-fifo   The presence of this property indicates hardware
 		     support for the external trigger stamp FIFO.
+  - little-endian    The presence of this property indicates the 1588 timer
+		     IP block is little-endian mode. The default endian mode
+		     is big-endian.
 
   These properties set the operational parameters for the PTP
   clock. You must choose these carefully for the clock to work right.