i40e/i40evf: find partition_id in npar mode

When in NPAR mode the driver instance might be controlling the base
partition or one of the other "fake" PFs.  There are some things that
can only be done by the base partition, aka partition_id 1.  This code
does a bit of work to find how many partitions are there per port and
what is the current partition_id.

Change-ID: Iba427f020a1983d02147d86f121b3627e20ee21d
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>