Add MMAP Audio Balance

Similar to adding Mono audio, this cl adds the audio balance settings
to MMAP Audio.

Bug:209521805
Test: Settings -> Accessibility -> Audio Adjustment -> Audio Balance
Use OboeTester and play outputs with various settings on the slider

Change-Id: I3269f6fe39b5f720da69739c49eb787e57f93b0a
diff --git a/media/libaaudio/src/Android.bp b/media/libaaudio/src/Android.bp
index 38bcb7c..f50b53a 100644
--- a/media/libaaudio/src/Android.bp
+++ b/media/libaaudio/src/Android.bp
@@ -214,6 +214,7 @@
         "flowgraph/MonoBlend.cpp",
         "flowgraph/MonoToMultiConverter.cpp",
         "flowgraph/MultiToMonoConverter.cpp",
+        "flowgraph/MultiToManyConverter.cpp",
         "flowgraph/RampLinear.cpp",
         "flowgraph/SampleRateConverter.cpp",
         "flowgraph/SinkFloat.cpp",