igb: remove microwire support from igb

igb doesn't have any devices that use a microwire interface for NVM.  As
such the code related to this can be removed.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>