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

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

Change-Id: I49da8e5ab24502d0de5c09b7fc9f4b8a51bead60
Audio_Effects: Add @hide to some fields and methods

Signed-off-by: mv <michvett.mv@gmail.com>
base: audiofx: harden against offload effects

Hack for now to allow using DSPManager for offload effects

-offload effect equalizer has only 5 bands but DSPManager has hardcoded 6
-offload effect bassboost doesnt support center freq

Change-Id: I9ad661221654415b2be3ed18f8cf31453d6df637
(cherry picked from commit 0191323bd51704bec2a9d81d53eb554e229814cd)