i40e: Move I40E_MASK macro to i40e_register.h

The macro is practically used only in i40e_register.h header file except
few I40E_MDIO_CLAUSE* macros that are defined in i40e_type.h
Move I40E_MASK macro to i40e_register.h header, I40E_MDIO_CLAUSE* macros
are refactored in subsequent patch.

Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>