i40e: introduce new dump desc XDP command

Interfaces already exist for dumping Rx and Tx descriptor information.
Introduce another for doing the same for XDP descriptors.

Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>