[Nouveau] All-round reclocking improvements

[Roy Spliet]

In bulletpoints:
- Add some support for G94 and G96 reclocking. Has been tested on literally
  two cards, which is hardly adequate as "full coverage". On the other hand, 
  the changes were small enough to make me confident this might work for others
  as well.
- Fix NV50 wait for VBLANK when no monitor is plugged in.
- Voltage related inprovements for GT21x.
- Slightly improve Keplers handling of DDR3 cards where the DLL should be
  disabled. Lays the foundation for a similar improvement in GDDR5 cards, but
  lacking such a card I can't test any changes here.

If you don't feel confident about patch 9 feel free to drop it. But better:
test this series and report with me on IRC #nouveau when things don't work.
Cheers,

Roy