libadf is a new member of VNDK

The library is used by both platform (e.g. libminui) and vendors (for
theor HW composer HAL impl).

Bug: 64050301
Test: 2017 pixel devices build
Test: libadf.so is in /system/lib[64]/vndk directory
Change-Id: I20b8b9728cdc56a7491266070740c3330d4324dc

adf/libadf/Android.bp

@@ -12,8 +12,12 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-cc_library_static {
+cc_library {
     name: "libadf",
+    vendor_available: true,
+    vndk: {
+        enabled: true,
+    },
     srcs: ["adf.cpp"],
     cflags: ["-Werror"],
     local_include_dirs: ["include"],