makefs: correct iso9660 Rock Ridge TF timestamps

The bit definitions for the TF_* timestamp bits (TF_MODIFY, etc.) were
incorrect, and timestamps were written in the wrong order.

See RRIP 4.1.6 Description of the "TF" System Use Entry for details.

PR: 203531
Reported by: Thomas Schmitt <scdbackup@gmx.net>
Reviewed by: jrtc27, kevans
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D39221