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: Ie55129109060a4a7862fee3177f994401e00b6c1
diff --git a/media/libmedia/Android.mk b/media/libmedia/Android.mk
index ac770f1..df6eb57 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 \