igb: enable auxiliary PHC functions for the i210

The i210 device offers a number of special PTP Hardware Clock features on
the Software Defined Pins (SDPs). This patch adds support for two of the
possible functions, namely time stamping external events, and periodic
output signals.

The assignment of PHC functions to the four SDP can be freely chosen by
the user.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>