Define HAL for audio effects

Created after hardware/audio_effect.h with the following changes:

 - names changed to satisfy HAL style guide;

 - defined an interface per effect, an interface method
   per command, and getter / setter methods for properties;

 - retained methods for executing proprietary commands
   and accessing proprietary properties, only to be used
   for third-party software effects;

 - HIDL vector type is used instead of count / array pairs;

 - provider callback changed to be used over RPC;

 - 'dump' is method is already defined by generated code.

Note that audio data is currently transferred using AudioBuffers,
which is not effective due to memory copy and HwBinder transaction
involved. The transfer method will be changed to FastMessageQueue.

Bug: 30222631
Test: make
Change-Id: Ic8ea5c19688610ebe642c7597d2bcfa3226977e7