Split audio effects headers

There can be different use cases with the code that imports
headers from audio_effects (each subsequent case is a more
specialized version of the previous one):

  1. The code only needs access to general structures
     like effect_descriptor_t:
     ==> include system/audio_effect.h
     Example: AudioSystem in libmedia

  2. The code that needs access to effect UUID and parameter
     enums:
     ==> include system/audio_effects/effect_foo.h
     Examples: media framework effects interfaces, libwilhelm

  3. The code that needs to call into HAL:
     ==> include hardware/audio_effect.h
     Examples: libaudiohal (implementation part) and libeffects

  4. The code that implements a particular effect:
     ==> include audio_effects/effect_foo.h
     Examples: cts/.../CTSTestEffect.cpp
               stuff in hardware/, vendor/

Note that AudioPolicy still deals with the effects HAL directly,
this needs to be fixed.

Change-Id: I963335ede6a196f9225caf21e1a01d03635e363c
Test: make
diff --git a/services/audioflinger/Threads.cpp b/services/audioflinger/Threads.cpp
index a35fdb2..e661a3b 100644
--- a/services/audioflinger/Threads.cpp
+++ b/services/audioflinger/Threads.cpp
@@ -33,12 +33,12 @@
 #include <utils/Trace.h>
 
 #include <private/media/AudioTrackShared.h>
-#include <audio_effects/effect_ns.h>
-#include <audio_effects/effect_aec.h>
 #include <audio_utils/conversion.h>
 #include <audio_utils/primitives.h>
 #include <audio_utils/format.h>
 #include <audio_utils/minifloat.h>
+#include <system/audio_effects/effect_ns.h>
+#include <system/audio_effects/effect_aec.h>
 #include <system/audio.h>
 
 // NBAIO implementations