We need this in userspace for interpreting some of the perf ctrs.

Note possibly not quite sufficient if we had some frequency mgmt
approach other than race-to-idle.  Not really sure what the best
thing to do if we did.  Although displaying results as a percentage
of max frequence seems sensible(ish) if we did.
Signed-off-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>