[Nouveau] [Patch] Add a custom power management perflvl

[Martin Peres]

Hi everyone,

Please comment on this patch allowing you to set all the PM-related 
clocks on the card. The patch is described in length in the commit log.

There is something some of you will like and some won't. The custom_* 
files will always contain the values of the current perflvl unless the 
user changed them after the latest reclock.
I may also add all the available voltage in sysfs in the same way Ben 
added all the available performance levels (performance_level_X).

If you no-one has anything against it, please push it to master.

Martin