e1000e: add support for IEEE-1588 PTP

Add PTP IEEE-1588 support and make accesible via the PHC subsystem.

v2: make e1000e_ptp_clock_info a static const struct per Stephen Hemminger

Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Reviewed-by: Jacob Keller <Jacob.e.keller@intel.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>