libAudioHal: factorize V2 and V4

Merge the two versions and ifdef the few
parts still different.

Test: playback music, assistant
Change-Id: I750f5d18ba34236637c18a87e2daa54a7c446d91
Signed-off-by: Kevin Rocard <krocard@google.com>
diff --git a/media/libaudiohal/Android.bp b/media/libaudiohal/Android.bp
index 3a5df27..0ff0d4a 100644
--- a/media/libaudiohal/Android.bp
+++ b/media/libaudiohal/Android.bp
@@ -8,6 +8,7 @@
 
     cflags: [
         "-Wall",
+        "-Wextra",
         "-Werror",
     ],