Added libaudioflinger_headers

Test: Builds libaudioflinger_headers
Bug: 202897137

Change-Id: I046cf1ab963ef62d64527bbcad129ff6ff0490ef
(cherry picked from commit 260c9cdd05b7e65dcd0dcfd88e3f4926cf8dc09c)
diff --git a/services/audioflinger/Android.bp b/services/audioflinger/Android.bp
index 420ae52..9cb30e2 100644
--- a/services/audioflinger/Android.bp
+++ b/services/audioflinger/Android.bp
@@ -114,3 +114,8 @@
     },
 
 }
+
+cc_library_headers {
+    name: "libaudioflinger_headers",
+    export_include_dirs: ["."],
+}