i40e: use new unified virtchnl header file

This patch changes the i40e driver to start using the new virtchnl
interface header file, and removes an already existing duplicate of the
i40e_virtchnl.h file contained in the i40e directory.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>