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

This device stores the number of seconds in a 32 bit register.  So
more work is needed on this driver before the year 2038 comes around.

Compile tested only.

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