lpm-stats: Optimize stats path

Stats for cpu and cluster exit path query the ktime for every level and
this increases the overall idle exit latency. Get the timestamp only
once and use the same information to populate into different level.

Change-Id: Iece36015910fcb16bd04a25dae1bf0396ab463e2
Signed-off-by: Archana Sathyakumar <asathyak@codeaurora.org>