Add neverallows for debugfs access

Android R launching devices and newer must not ship with debugfs
mounted. For Android S launching devices and newer, debugfs must only be
mounted in userdebug/eng builds by init(for boot time initializations)
and dumpstate(for grabbing debug information from debugfs using the
dumpstate HAL).

This patch adds neverallow statements to prevent othe processes
being provided access to debugfs when the flag PRODUCT_SET_DEBUGFS_RESTRICTIONS
is set to true.

Test: make with/without PRODUCT_SET_DEBUGFS_RESTRICTIONS
Bug: 184381659
Change-Id: I63a22402cf6b1f57af7ace50000acff3f06a49be
diff --git a/private/dumpstate.te b/private/dumpstate.te
index 13e3b4c..f418fa3 100644
--- a/private/dumpstate.te
+++ b/private/dumpstate.te
@@ -54,7 +54,10 @@
 }:process signal;
 
 # For collecting bugreports.
-allow dumpstate debugfs_wakeup_sources:file r_file_perms;
+no_debugfs_restriction(`
+  allow dumpstate debugfs_wakeup_sources:file r_file_perms;
+')
+
 allow dumpstate dev_type:blk_file getattr;
 allow dumpstate webview_zygote:process signal;
 allow dumpstate sysfs_dmabuf_stats:file r_file_perms;