igb: Refactoring of i210 file.

This patch refactors the functions in e1000_i210.c in order to remove need
for prototypes.

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