Allow system_server to search su:key in debuggable build

Test: successful fs-verity setup with key loaded from shell
Bug: 112037636
Change-Id: Ide01d11f309008fffeafdedb517508db94472873
diff --git a/private/system_server.te b/private/system_server.te
index 8aa7785..6fa2ae6 100644
--- a/private/system_server.te
+++ b/private/system_server.te
@@ -798,6 +798,9 @@
 };
 # Allow system process to access the keyring.
 allow system_server kernel:key search;
+userdebug_or_eng(`
+  allow system_server su:key search;
+')
 
 # Postinstall
 #