[3/3] AudioEffect: Add a stereo widener effect

Change-Id: Iab2035c5601394b060e7e77e85ad85aca6e4c89f
[3/3] AudioFX: Add center frequency param to bassboost

Change-Id: I49da8e5ab24502d0de5c09b7fc9f4b8a51bead60
Merge "[3/3] AudioFX: Add center frequency param to bassboost" into kk44