cpufreq: schedutil: Keep track of average policy capacity

Average policy capacity will be used in future patches to improve detection
of hispeed load condition.

Change-Id: Icab992243b83eb5feaae619d16b22510010f54c5
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>
[avilaj@codeaurora.org: Fix merge conflicts caused by moving around tracepoint patch]
Signed-off-by: Jonathan Avila <avilaj@codeaurora.org>