ixgbe: Add support for newer thermal alarm

The newer copper PHY implementation used with newer X550EM_x
devices uses a different thermal alarm type than the earlier
one. Make changes to support both types.

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>