tracing: power: Add trace events for bw_hwmon

The bw_hwmon_meas trace event is to log measurement details and the
bw_hwmon_update trace event is to log the final decision.

Change-Id: I839ace50b1f1686227bcbf7d38a75f89092d26b1
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>