Factor out buffer provider code from AudioMixer

In preparation for playback rate support and timestretching.

Bug: 19196501
Change-Id: I435accb852d32110dd0b3a9917488522c567ba80
diff --git a/services/audioflinger/Android.mk b/services/audioflinger/Android.mk
index fee2347..f8446ac 100644
--- a/services/audioflinger/Android.mk
+++ b/services/audioflinger/Android.mk
@@ -44,9 +44,9 @@
     SpdifStreamOut.cpp          \
     Effects.cpp                 \
     AudioMixer.cpp.arm          \
-    PatchPanel.cpp
-
-LOCAL_SRC_FILES += StateQueue.cpp
+    BufferProviders.cpp         \
+    PatchPanel.cpp              \
+    StateQueue.cpp
 
 LOCAL_C_INCLUDES := \
     $(TOPDIR)frameworks/av/services/audiopolicy \