selinux: add security in-core xattr support for pstore and debugfs

- add "pstore" and "debugfs" to list of in-core exceptions
- change fstype checks to boolean equation
- change from strncmp to strcmp for checking

Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
[PM: tweaked the subject line prefix to "selinux"]
Signed-off-by: Paul Moore <pmoore@redhat.com>