msm: ipa2: add active clients logging

add framework for IPAv2 active clients history logging
logging is enabled by default
cat /sys/kernel/debugfs/ipa/active_clients in order to view logs
echo anything to /sys/kernel/debugfs/ipa/active_clients in order
to clear the history log buffer

Change-Id: I975271798aee56ac9889d34203a32c99a30fc958
Signed-off-by: Valery Gorohovsky <valeryg@codeaurora.org>