Add VINTF manifest for android.system.keystore2

A VINTF manifest is required for services that expose VINTF stability
interfaces. Now that libbinder_rs supports stability, we need to update
this usage.

Test: m && adb shell start keystore2
Bug: 179907868
Change-Id: I9d3b363c6315bace145385867a5c495bb9051870
diff --git a/keystore2/Android.bp b/keystore2/Android.bp
index 9875d64..273bdd7 100644
--- a/keystore2/Android.bp
+++ b/keystore2/Android.bp
@@ -94,4 +94,6 @@
         "libvpnprofilestore-rust",
     ],
     init_rc: ["keystore2.rc"],
+
+    vintf_fragments: ["android.system.keystore2-service.xml"],
 }