- added DISABLED state to FSM to explicitely sit in DISABLED state
  when the mechanism is not enabled (before it was in reset/ALLOW)
- changed std_logic_vectors to unsigned in number of places, this
  made the code more readable and concise
- defined constants with zero latency (instead of having signal)
- added delay to latency calculation so that the latency introduced
  by gc_sync_ffs is accounted for