access_vectors: add lockdown class

Needed to support upstream patch
https://github.com/torvalds/linux/commit/59438b46471ae6cdfb761afc8c9beaf1e428a331

Bug: 148822198
Test: compiles
Change-Id: I304c1a97c12067dd08d4ceef93702101908012ed
diff --git a/private/security_classes b/private/security_classes
index c0631e9..04ed814 100644
--- a/private/security_classes
+++ b/private/security_classes
@@ -141,6 +141,9 @@
 
 class perf_event
 
+# Introduced in https://github.com/torvalds/linux/commit/59438b46471ae6cdfb761afc8c9beaf1e428a331
+class lockdown
+
 # Property service
 class property_service          # userspace