iavf: Refactor iavf state machine tracking

Replace state changes of iavf state machine
with a method that also tracks the previous
state the machine was on.

This change is required for further work with
refactoring init and watchdog state machines.

Tracking of previous state would help us
recover iavf after failure has occurred.

Signed-off-by: Jakub Pawlak <jakub.pawlak@intel.com>
Signed-off-by: Jan Sokolowski <jan.sokolowski@intel.com>
Signed-off-by: Mateusz Palczewski <mateusz.palczewski@intel.com>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>