i40e: use alloc_workqueue instead of create_singlethread_workqueue

Replace calls to create_singlethread_workqueue instead with alloc_workqueue
as is style with other Intel drivers. This provides more control over
workqueue creation, and allows explicit setting of the desired mode of
operation. It also makes it more obvious that driver name constant is
passed to a format "%s".

Change-ID: I6192b44caf5140336cd54c5b350d51c73b541fdb
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>