Fix perfprofd denial (simpleperf debugfs read).

Bug: http://b/23814810
Change-Id: I731bd70ec982e47b86befb32a9edcb71570e9d64

perfprofd.te

@@ -47,6 +47,9 @@ userdebug_or_eng(`
   # to see whether it has a build ID
   allow perfprofd exec_type:file r_file_perms;
 
+  # simpleperf examines debugfs on startup to collect tracepoint event types
+  allow perfprofd debugfs:file r_file_perms;
+
   # simpleperf is going to execute "sleep"
   allow perfprofd toolbox_exec:file rx_file_perms;