Reduce more power advisor churn

* Use chrono time types consistently to avoid a bug with comparing
  milliseconds with nanoseconds
* Change the update imminent timeout callback to use a while loop
  instead of an if-statement to guard against spurious wakeups.

Saves 2% of instructions and ~5% of cpu cycles

Bug: 231628914
Test: bouncy ball

Change-Id: Id61020e60825347dcf94794b92f8bc04c1455cfa