audio: support equalizer to fix VtsHalAudioEffectFactoryTargetTest
See each invidivual commit for details.
Basically, this reduces VtsHalAudioEffectFactoryTargetTest from 8 failures to 1 failure.
The remaining one requires us to implement other effects, which are also not implemented in the
reference stub hal (com.android.hardware.audio
).
Bug: TIAU-524