audiohal: Support stateful downmixer effects

Fraunhofer's downmixer has additional buffering, this is incompatible
with how DownmixerBufferProvider used to process incomplete buffers.

Now the effects HIDL wrapper delivers frameCount updates in
audiobuffers to the server side. This fixes playback of multichannel
sound streams.

Bug: 36181621
Test: play 5.1 track from Play Music
Change-Id: I3b2cd097d61873c6ba329f1a574235ac88b21cac
diff --git a/media/libaudiohal/EffectHalHidl.h b/media/libaudiohal/EffectHalHidl.h
index c8db36f..0d011aa 100644
--- a/media/libaudiohal/EffectHalHidl.h
+++ b/media/libaudiohal/EffectHalHidl.h
@@ -92,6 +92,7 @@
 
     status_t getConfigImpl(uint32_t cmdCode, uint32_t *replySize, void *pReplyData);
     status_t prepareForProcessing();
+    bool needToResetBuffers();
     status_t processImpl(uint32_t mqFlag);
     status_t setConfigImpl(
             uint32_t cmdCode, uint32_t cmdSize, void *pCmdData,