i40e: Add functions which apply correct PHY access method for read and write operation

Depending on external PHY type, register access method should be
different. Clause22 or Clause45 can be chosen for different PHYs.
Implemented functions apply correct access method for used device.

Change-ID: If39d5f0da9c0b905a8cbdc1ab89885535e7d0426
Signed-off-by: Michal Kosiarz <michal.kosiarz@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>