Build libmedia_omx with BOARD_VNDK_VERSION

Add dependency to libstagefright_headers.

Bug: 37342627
Test: BOARD_VNDK_VERSION=current m -j libmedia_omx
Change-Id: Ia97a981d4cd04acbdc3df6dac63db3f18af21a03
diff --git a/media/libmedia/Android.bp b/media/libmedia/Android.bp
index 521dc5f..b180853 100644
--- a/media/libmedia/Android.bp
+++ b/media/libmedia/Android.bp
@@ -2,6 +2,8 @@
     name: "libmedia_headers",
     vendor_available: true,
     export_include_dirs: ["include", "omx/1.0/include"],
+    header_libs: ["libstagefright_headers"],
+    export_header_lib_headers: ["libstagefright_headers"],
 }
 
 cc_library {