Provide VINTF for Trusty Keymaster

This makes it easier to add or remove the Trusty keymaster service from
a device by providing a manifest fragment to add whenever it is enabled.

Test: Keymaster VTS, Keystore CTS (sans attestation)
Change-Id: Ib0f5fd7c016c0c18d77c9d2623c89f3b35ba7ad7
diff --git a/trusty/keymaster/Android.bp b/trusty/keymaster/Android.bp
index 3a9beaf..f32a69e 100644
--- a/trusty/keymaster/Android.bp
+++ b/trusty/keymaster/Android.bp
@@ -136,4 +136,6 @@
         "libkeymaster4",
         "android.hardware.keymaster@4.0"
     ],
+
+    vintf_fragments: ["4.0/android.hardware.keymaster@4.0-service.trusty.xml"],
 }