Add sepolicy for the securityfs mount type.

See discussion in aosp/1233645. There was a concern about this
filesystem automounting when enabled, so this change adds sepolicy to
preemptively lock it down.

I'm not confident it actually automounts. If it does, it'll land in
/sys/kernel/security, which is also protected with the sysfs policy.

Test: Builds
Bug: 148102533
Change-Id: I78a246a5c18953f2471f84367ab383afb2742908
3 files changed