More fixes to the AudioDSP

Recover from partial sync with CyanogenMod. Sync to version 7:
 - do not use thumb instruction set for AudioDSP
 - fix up types at AudioDSP to optimal
 - workaround low-volume rattling with AudioMixer's volume ramping.

Various fixes.
- speed up estimateLevel
- remove state from estimateLevel, as it may be used by multiple
  tracks simultaneously.
- co-opt android's volum ramping mechanism to smoothly apply the
  envelope for me.
- fix loud snap when enabling headphone effect by clearing the
  allocated allpass buffer.