Use callbacks for Midi I/O

Instead of having the Sonivox engine directly open the file and
use stdio to read from it, use caller-provided callbacks.

Change-Id: I4d775c8458c48c591a15794c4517e006dcf034e1
diff --git a/media/libmedia/Android.mk b/media/libmedia/Android.mk
index bcec9c9..c58a503 100644
--- a/media/libmedia/Android.mk
+++ b/media/libmedia/Android.mk
@@ -42,6 +42,7 @@
     mediarecorder.cpp \
     IMediaMetadataRetriever.cpp \
     mediametadataretriever.cpp \
+    MidiIoWrapper.cpp \
     ToneGenerator.cpp \
     JetPlayer.cpp \
     IOMX.cpp \