[audio][spdif] Add spdif AC3 make to audio_utils make

Recursively build libraries under audio_utils to resolve
dependencies properly for HAL.

This is part of support for AC3 passthrough over HDMI.

Bug: 9428304
Change-Id: I2e3067dbe9b28dc5ea9eb0e9faebe31f8d9e4135
Signed-off-by: Phil Burk <philburk@google.com>
diff --git a/audio_utils/Android.mk b/audio_utils/Android.mk
index 994cc45..3a30562 100644
--- a/audio_utils/Android.mk
+++ b/audio_utils/Android.mk
@@ -67,3 +67,6 @@
 #LOCAL_SHARED_LIBRARIES := libaudioutils
 
 include $(BUILD_HOST_STATIC_LIBRARY)
+
+include $(call all-makefiles-under,$(LOCAL_PATH))
+