dt-binding: ptp_qoriq: support fsl,tmr-fiper3 property

Add fsl,tmr-fiper3 property definition which is supported only
on DPAA2 and ENETC network controller hardware.

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