net:phy:dp83640: Initialize PTP clocks at device init.

The trigger and events functionality can be useful even if packet
timestamping is not used, but the required PTP clock is only enabled
when packet timestamping is started. This patch moves the clock enable
to when the interface is configured.

Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>