SELinux: enable processes with mac_admin to get the raw inode contexts

Enable processes with CAP_MAC_ADMIN + mac_admin permission in policy
to get undefined contexts on inodes.  This extends the support for
deferred mapping of security contexts in order to permit restorecon
and similar programs to see the raw file contexts unknown to the
system policy in order to check them.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>