Log statistics on CPU usage in Hz in addition to wall clock time
Use CPU statistics for all playback threads, not just MIXER
(but they are disabled by default by a compile-time debug macro).
ThreadCpuUsage library:
- Move statistics out of the library and leave that up to the caller
- Add API to determine a CPU's frequency
Change-Id: Ia1011123146e641fcf210ef26e78ae2b4d3b64ad