iavf: Remove timer for work triggering, use delaying work instead

Remove the watchdog timer, instead declare watchdog task
as delayed work and use dedicated workqueue to service driver
tasks. The dedicated driver workqueue iavf_wq is common
for all driver instances.

Signed-off-by: Jakub Pawlak <jakub.pawlak@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>