audiohal: Fix volume changes handling

Some legacy implementations of the effects HAL use the condition
of the reply buffer being NULL as an indication that they shouldn't
apply attenuation to the input audio data. Therefore, separate
methods are needed to distinguish the use cases of delegating the
volume control to the effect, and just informing the effect of the
volume changes.

A new method added to IEffect: volumeChangeNotification that implements
the second use case. The contract of setAndGetVolume method has been
updated to indicate that it is only called in the first use case.

Also updated the wrapper for a generic IEffect commands to pass NULL
pointers to the command and reply buffers in case when the size
of the input or output data is 0, to preserve compatibility with
direct calls from the framework.

Bug: 34368451
Test: volume control works when both Bass Boost and Equalizer are
      enabled in the NXP implementation of the effects

Change-Id: I3c9a5bbdff561802bc94080c51703385a8903282