Convert tty common code to use make_dev_s().

Tty.c was untypical in that it handled the si_drv1 issue consistently
and correctly, by always checking for si_drv1 being non-NULL and
sleeping if NULL. The removed code also illustrated unneeded
complications in drivers which are eliminated by the use of new KPI.

Reviewed by: hps, jhb
Discussed with: bde
Sponsored by: The FreeBSD Foundation
MFC after: 3 weeks
Differential revision: https://reviews.freebsd.org/D4746