Make software codecs as VNDK

Software codecs and their dependencies are marked as VNDK (or just
vendor_available:true for static/header libs).

Bug: 37343418
Test: build the software codecs with BOARD_VNDK_VERSION=current
Change-Id: I9ace2ba9f30e711b1d14840cb8300f467621cde4
diff --git a/Android.bp b/Android.bp
index e9e3f98..6deb4d9 100644
--- a/Android.bp
+++ b/Android.bp
@@ -1,5 +1,9 @@
 cc_library_shared {
     name: "libvorbisidec",
+    vendor_available: true,
+    vndk: {
+        enabled: true,
+    },
 
     srcs: [
         "Tremolo/bitwise.c",