ptp: Add a driver for InES time stamping IP core.

The InES at the ZHAW offers a PTP time stamping IP core.  The FPGA
logic recognizes and time stamps PTP frames on the MII bus.  This
patch adds a driver for the core along with a device tree binding to
allow hooking the driver to MII buses.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>