ProcessStats: Handle changes in the scaling frequnency

Switching from MP to IKS mode results increase in number of operating points
and results in bug #1183781 . The patch makes sure that whenever the available
scaling frequency changes it resets the existing values and sets them as per the
new values.

Change-Id: Ic74cdc2015f3c4ddd61cb116d1f4b4ed1204a3bf
Signed-off-by: Vishal Bhoj <vishal.bhoj@linaro.org>