Add libmedia_headers library.

Bug: 33241851
Test: build with BOARD_VNDK_VERSION := current
Change-Id: I6239b58890cabae69f27daf14aa2fb19d8bffe5d
diff --git a/media/libmedia/Android.bp b/media/libmedia/Android.bp
index 4b14543..772555d 100644
--- a/media/libmedia/Android.bp
+++ b/media/libmedia/Android.bp
@@ -1,3 +1,9 @@
+cc_library_headers {
+    name: "libmedia_headers",
+    vendor_available: true,
+    export_include_dirs: ["include"],
+}
+
 cc_library {
     name: "libmedia_helper",
     srcs: ["AudioParameter.cpp", "TypeConverter.cpp"],