i40e: Prep i40e header for aux bus conversion

Add the definitions to the i40e client header file in
preparation to convert i40e to use the new auxiliary bus
infrastructure. This header is shared between the 'i40e'
Intel networking driver providing RDMA support and the
'irdma' driver.

Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>