i40e/i40evf: add GetStatus command for nvmupdate

This adds a new GetStatus command so that the NVM update tool can query
the current status instead of doing fake write requests to probe for
readiness.

Change-ID: I671ec6ccd4dfc9dbac3a03b964589d693fda5cd8
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>