igb: Remove GS40G specific defines/functions

The I210 internal PHY can be accessed just as well with the access
functions shared by 82580, I350, and I354 devices. A side effect of
relying on the common functions, is that I210 cable length support
is folded back into the common case which effectively reverts the
following commit:

    commit 59f30104
    Author: Carolyn Wyborny <carolyn.wyborny@intel.com>
    Date:   Wed Oct 10 04:42:59 2012 +0000

    igb: Update get cable length function for i210/i211

Cc: Carolyn Wyborny <carolyn.wyborny@intel.com>
Signed-off-by: Aaron Sierra <asierra@xes-inc.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>