AAudio: add group in headers for doxygen

This is needed for proper navigation in the NDK reference docs.

Bug: 36995264
Test: Look at NDK docs after staging. Audio link should work.
Change-Id: Ifb61f95d536310a420d90f32c64557b75901d751
Signed-off-by: Phil Burk <philburk@google.com>
diff --git a/media/libaaudio/include/aaudio/AAudioDefinitions.h b/media/libaaudio/include/aaudio/AAudioDefinitions.h
index 846318c..fbd284c 100644
--- a/media/libaaudio/include/aaudio/AAudioDefinitions.h
+++ b/media/libaaudio/include/aaudio/AAudioDefinitions.h
@@ -14,6 +14,15 @@
  * limitations under the License.
  */
 
+/**
+ * @addtogroup Audio
+ * @{
+ */
+
+/**
+ * @file AAudioDefinitions.h
+ */
+
 #ifndef AAUDIO_AAUDIODEFINITIONS_H
 #define AAUDIO_AAUDIODEFINITIONS_H
 
@@ -117,3 +126,5 @@
 #endif
 
 #endif // AAUDIO_AAUDIODEFINITIONS_H
+
+/** @} */