- Current testing shows that (ab)using the JBC performance counter in bus

- Current testing shows that (ab)using the JBC performance counter in bus
  cycle mode as timecounter just works fine. My best guess is that a firmware
  update has fixed this, check at run-time whether it advances and use a
  positive quality if it does. The latter will cause this timecounter to be
  used instead of the tick counter based one, which just sucks for SMP.
- Remove a redundant NULL assignment from the timecounter initialization.