Battery stats: track actually running time

Use the uptime while creating the battery stats history to
generate a new event indicating when the CPU is actually running.
We can do this in combination with the new event reporting when
the CPU comes awake, looking at the difference between the
uptime and elapsed time at that point to determine when it last
when to sleep.

Also use this information to generate a new set of aggregated
states, the uptime caused by each wake reason.

Finally use new radio down timestamp to adjust the times we
compute for radio use.  Note that this information is not (yet)
being used to adjust how these are recorded in the history.

Change-Id: I723b3b526c8e7d64de0cac9d1193e04132d5a3e4