SELinux permissions for gatekeeper TEE proxy

sets up:
- execute permissions
- binder permission (system_server->gatekeeper->keystore)
- prevents dumpstate and shell from finding GK binder service
- neverallow rules for prohibited clients

Change-Id: I1817933a91de625db469a20c7a4c8e2ca46efa1e
diff --git a/file_contexts b/file_contexts
index 45a3549..7ef7b3c 100644
--- a/file_contexts
+++ b/file_contexts
@@ -147,6 +147,7 @@
 /system/bin/mdnsd	u:object_r:mdnsd_exec:s0
 /system/bin/installd	u:object_r:installd_exec:s0
 /system/bin/keystore	u:object_r:keystore_exec:s0
+/system/bin/gatekeeperd u:object_r:gatekeeperd_exec:s0
 /system/bin/debuggerd	u:object_r:debuggerd_exec:s0
 /system/bin/debuggerd64	u:object_r:debuggerd_exec:s0
 /system/bin/wpa_supplicant	u:object_r:wpa_exec:s0