msm:rq_stats: Register for Cpufreq policy notification

Currently the load of the system is calculated using the max
frequency that is read during startup(It does not get updated
when the policy changes). As a result, the average load of the
system is incorrectly calculated and the system might not bring
the cpus online to manage the additional load. This
reduces the performance of the system.

To fix this issue, register rq_stats to receive cpufreq policy
notifications. Update the policy's max frequency when a
notification is received and use that value to calculate the load.

Change-Id: Icc78e28c736c170e198f723fd96c13dfb2dafe8a
Signed-off-by: Archana Sathyakumar <asathyak@codeaurora.org>
Signed-off-by: Anji Jonnala <anjir@codeaurora.org>