iavf: remove references to old names

Remove the register name references to I40E_VF* and change to
IAVF_VF. Update the descriptor names and defines to the IAVF
name.

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>