i40e: dump VF information in debugfs

Dump some internal state about VFs through debugfs. This provides
information not available with 'ip link show'. To use, write "dump vf
<id>" to the command file, or just "dump vf" to dump information on all
of the VFs.

Change-ID: Ibe32b7f4ae55d4358c0b903217475f708ada1ecd
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>