Update make file for vndk enabled.

Update the Android.bp generated with hidl-gen.

Test: build with and without BOARD_VNDK_VERSION=current
Bug: 63866913
Change-Id: I1a9db1df49e0f13c5790da2b118ae9ec63ba34a7
diff --git a/audio/2.0/Android.bp b/audio/2.0/Android.bp
index b141951..cdaaa15 100644
--- a/audio/2.0/Android.bp
+++ b/audio/2.0/Android.bp
@@ -88,6 +88,9 @@
     generated_headers: ["android.hardware.audio@2.0_genc++_headers"],
     export_generated_headers: ["android.hardware.audio@2.0_genc++_headers"],
     vendor_available: true,
+    vndk: {
+        enabled: true,
+    },
     shared_libs: [
         "libhidlbase",
         "libhidltransport",