dpaa_eth: add support for hardware timestamping

This patch is to add hardware timestamping support
for dpaa_eth. On Rx, timestamping is enabled for
all frames. On Tx, we only instruct the hardware
to timestamp the frames marked accordingly by the
stack.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Acked-by: Madalin Bucur <madalin.bucur@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>