igb: support EXTTS on 82580/i354/i350

Support for the PTP pin function on 82580/i354/i350 based adapters.
Because the time registers of these adapters do not have the nice split in
second rollovers as the i210 has, the implementation is slightly more
complex compared to the i210 implementation.

Signed-off-by: Ruud Bos <kernel.hbk@gmail.com>
Tested-by: Gurucharan G <gurucharanx.g@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>