ptp: xgbe: convert to the 64 bit get/set time methods.

This driver's clock is implemented using a timecounter, and so with
this patch the driver is ready for the year 2038.

Compile tested only.

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