msm: lpm-levels: Modify ftrace events to track latency/sleep time

cpuidle enter and exit ftrace events can mismatch if lpm driver falls
back after choosing a low power mode. Modify ftrace events to clearly
distinguish between cpu power select event and cpuidle enter event.

Change-Id: I81bc2b175264c6bdeec555b2b1271c0f40870b1b
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>