igb: Make arrays on stack static const to avoid reallocation

While addressing the pin problem I noticed that all of the pin register
values where having to be pushed onto the stack each time the function was
called.  To avoid that I am making them static const so that they should
only need to be allocated once and we can avoid all the instructions to get
them onto the stack..

size before:
   text	   data	    bss	    dec	    hex	filename
 161477	  10512	      8	 171997	  29fdd	drivers/net/ethernet/intel/igb/igb.ko

size after:
   text	   data	    bss	    dec	    hex	filename
 161205	  10512	      8	 171725	  29ecd	drivers/net/ethernet/intel/igb/igb.ko

Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>