makefs: set cd9660 Rock Ridge timestamps for . and ..

DOT and DOTDOT entries have special handling, and previously only Rock
Ridge PX (POSIX attributes) entries were attached. Add TF (timestamp)
entries as well.

PR: 203531
Reported by: Thomas Schmitt <scdbackup@gmx.net>
Reviewed by: markj
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D39662