i40e/i40evf: clear aq bah-bal on shutdown

Clear the AQ BAH and BAL registers on a clean shutdown to help make sure
all is tidy when the driver is done.

Change-ID: I393e92680247daa52a8e00bab183213672d73578
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>