iavf: Refactor init state machine

Cleanup of init state machine, move state specific
code to separate functions and rewrite the
iavf_init_task() function.

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>