selinux: quiet the filesystem labeling behavior message

While the filesystem labeling method is only printed at the KERN_DEBUG
level, this still appears in dmesg and on modern Linux distributions
that create a lot of tmpfs mounts for session handling, the dmesg can
easily be filled with a lot of "SELinux: initialized (dev X ..."
messages.  This patch removes this notification for the normal case
but leaves the error message intact (displayed when mounting a
filesystem with an unknown labeling behavior).

Reported-by: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Paul Moore <pmoore@redhat.com>