i40e/i40evf: Add WB_ON_ITR offload support

X722 has a way to work around the descriptor WB issue,
this offload helps turn that feature on.

Change-ID: I7ffa67622426bfca5a651417b63e3afcfeb60412
Signed-off-by: Anjali Singhai Jain <anjali.singhai@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>