Fix GKI timers to take execution time into account

Previously, the GKI timer system would not take the time taken for
updating the timers into account when re-scheduling the next timer. This
would by design introduce timer drift into the system.

This patch measures the time taken for an alarm to be triggered to
report the correct number of ticks to the GKI timer subsystem, as well
as measuring the time taken for updating the timers to adjust the next
alarm accordingly.

This patch dramatically improves A2DP audio quality on various devices
which currently suffer timer drift problems.

Change-Id: Ia99454abcb2a6889c47b1d8e267705f29ebe7b64