Improve power tracking of WIFI use.

We now distribute "wifi started" time across all apps that are
holding WIFI locks that cause it to be started.  But only when
WIFI would not normally be running.  Also have a mechanism to
distribute other WIFI work that has happened across those processes
based on their use.

Also fixed a bug where we were not retaining the CPU speed step
stats across boots...!

Change-Id: I00e3153b98429166273750512cc37e7975211ab9