i40e: allow for more VSIs

The number of VSIs that the firmware reports to us is a guaranteed
minimum, not an absolute maximum. The hardware actually supports far
more  than the reported value, which we often need.

To allow for this, we allocate space for a larger number of VSIs than is
guaranteed by the firmware, with the knowledge that we may fail to get
them all in the future.

Note that we are just allocating pointers here, the actual (much larger)
VSI structures are allocated on demand.

Change-ID: I6f4e535ce39d3bf417aef78306e04fbc7505140e
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>