Add support for scaling mode parameter

Support VISUALIZER_PARAM__SCALING_MODE parameter.

Modify process() function to use new volume scaling parameter,
 used to set whether captured values are maximized by current
 headroom in the buffer (default existing behaviora) or left
 as is and thus affected by volume.

Modify AudioEffect to allow subclasses to override the following
 events: control status changed, enable status changed, command
 executed.
In Visualizer class (a subclass of AudioEffect), reset the
 scaling mode and capture size on the actual effect
 as cached when control is regained.
 This will allow the effect to be properly
 configured whenever Visualizers with different scaling
 modes or capture sizes are released (e.g. from java
 release() method).

Change-Id: I05cb9f925a296dceca91bafa9fe294ef2b2c2bd5