Disable multithreaded dexopt by default

* There is still a race condition here.
* Power users can re-enable this by setting
  persist.sys.dalvik.multithread to true

Change-Id: I03686bafbac1859695466fcb522bc5436ec82e0d
MusicFX: introduce MusicFX

If MusicFX is enabled, dsp must not build
but dsp must be enabled for all other devices.

Change-Id: Ic9d039f480a60f970b1b6b8d3ace0fb10de53c29