msm_mpdecision: directly access rq_stats and eliminate msm_rq_stats
The original purpose of msm_rq_stats is enabling userspace access to
rq_stats and comes with the overhead of additional spin/mutex
locks and sysfs facilities,  mainly used by userspace mpdecision.
However, kernel-based mpdecision still depends on this code to obtain
cpu load averages while using a tiny fraction of the code. This commit
completely eliminates msm_rq_stats code and adds a very simple
rq_stats direct-access capability in msm_mpdecision.