msm: hotplug: Allow to disable the circular stats buffer

This option reduces latency a tiny bit more.
msm: rq_stats: Calculate load based on current freq limit

We are not using rq_stats any more so this commit is just for the
sake of completeness.  Prior to this patch, load has been calculated
based on an initial value of policy.cpuinfo.max_freq. This value may
change for several reasons: userspace settings, thermal throttling
(hello hammerhead!) or extended frequency tables where the absolute
maximum level is often not used during regular operations. This
results in unreliable calculations. Consider current policy.max to
fix this behaviour.