i40e: Move DDP specific macros and structures to i40e_ddp.c

Move several DDP related macros and structures from i40e.h header
to i40e_ddp.c where are privately used. Make static i40e_ddp_load()
function that is also used only in i40e_ddp and move declaration of
i40e_ddp_flash() used by i40e_ethtool.c to i40e_prototype.h

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>