keymint: Add instance name

Bug: 179459878
Change-Id: I7b32b49d3eafaceda1ef494bc2ef2a2e5feffd26
diff --git a/citadel/service_contexts b/citadel/service_contexts
new file mode 100644
index 0000000..76c3122
--- /dev/null
+++ b/citadel/service_contexts
@@ -0,0 +1 @@
+android.hardware.security.keymint.IKeyMintDevice/strongbox  u:object_r:hal_keymint_service:s0