igb: call igb_ptp_suspend during suspend/resume cycle

Properly stop the extra workqueue items and ensure that we resume
cleanly. This is better than using igb_ptp_init and igb_ptp_stop since
these functions destroy the PHC device, which will cause other problems
if we do so. Since igb_ptp_reset now re-schedules the work-queue item we
don't need an equivalent igb_ptp_resume in the resume workflow.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>