ixgbe: Update PTP to support X550EM_x devices

The X550EM_x devices handle clocking differently, so update the
PTP implementation to accommodate them. This involves significant
changes to ixgbe's PTP code to accommodate the new range of
behaviors including things like non-power-of-2 clock wrapping.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Darin Miller <darin.j.miller@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>