Add test_pkvm_tee_service example tee service

It can be used to test that custom smcs filtering is correctly
integrated on devices with pkvm hypervisor.

Bug: 360102915
Test: vm run-microdroid --tee_services test_pkvm_tee_service
Test: builds
Change-Id: I10ccc42d754b2b16139d6c3b22754a1d3cbc76a3
diff --git a/private/tee_service_contexts b/private/tee_service_contexts
index 3791876..89eceae 100644
--- a/private/tee_service_contexts
+++ b/private/tee_service_contexts
@@ -7,3 +7,7 @@
 # <tee_service_name> <label>
 #
 # <tee_service_name> must be a string
+
+# Example tee service that can be used for end-to-end integration of
+# custom smcs filtering on devices with pkvm hypervisor.
+test_pkvm_tee_service u:object_r:test_pkvm_tee_service:s0