dt-binding: ptp_qoriq: support DPAA2 PTP compatible

Add a new compatible for DPAA2 PTP.
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

@@ -4,6 +4,7 @@ General Properties:
 
   - compatible   Should be "fsl,etsec-ptp" for eTSEC
                  Should be "fsl,fman-ptp-timer" for DPAA FMan
+                 Should be "fsl,dpaa2-ptp" for DPAA2
                  Should be "fsl,enetc-ptp" for ENETC
   - reg          Offset and length of the register set for the device
   - interrupts   There should be at least two interrupts. Some devices