Abstract away access to audio effects HAL and factory

In this CL all direct calls to functions from EffectsFactoryApi.h
and hardware/audio_effect.h are encapsulated within two new
classes: EffectsFactoryHalLocal and EffectHalLocal. AudioFlinger
uses interface classes EffectsFactoryHalInterface and
EffectHalInterface to access these functions.

Bug: 30222631
Change-Id: Id64b9c5529319077f6f968921489a13f60daa977