Add permissions to modify raw_syscall filters.

These are to be used by traced in order to support tracing only a subset
of all syscalls when using raw_syscall ftrace events. Currently, the
associated files are only accessible in userdebug via selinux, so the
corresponding chmods are userdebug-only too.

Test: locally on-device with perfetto
Change-Id: Ifc6def54ad269c3e09eda268c697b89f2b940baf