Eliminate dependencies on hardware/audio.h (trivial cases)

frameworks/av must not depend on hardware/ (except for the code
from libaudiohal that actually calls into HAL).

This CL deals with simple cases where depending on system/audio.h
is enough.

Change-Id: Ia2cb66cc8c92316ce5ab884a008d5e531263c2e4
Test: make
diff --git a/services/audioflinger/SpdifStreamOut.cpp b/services/audioflinger/SpdifStreamOut.cpp
index b9260f8..a44ab2a 100644
--- a/services/audioflinger/SpdifStreamOut.cpp
+++ b/services/audioflinger/SpdifStreamOut.cpp
@@ -17,7 +17,7 @@
 
 #define LOG_TAG "AudioFlinger"
 //#define LOG_NDEBUG 0
-#include <hardware/audio.h>
+#include <system/audio.h>
 #include <utils/Log.h>
 
 #include <audio_utils/spdif/SPDIFEncoder.h>