MFC tty fixes, r259549 and r259663

Keep tty_makedev as a function to preserve the KBI on 10-stable
(it is a macro in CURRENT). The changes for this are direct
commits to 10-stable.

r259549 (glebius):
- Rename tty_makedev() into tty_makedevf() and make it capable
to fail and return error.
- Use make_dev_p() in tty_makedevf() instead of make_dev_cred().
- Always pass MAKEDEV_CHECKNAME flag.
- Optionally pass MAKEDEV_REF flag.
- Provide macro for compatibility with old API.

This fixes races with simultaneous creation and desctruction of
ttys, and makes it possible to call tty_makedevf() from device
cloners.

A race in tty_watermarks() still exist, since the latter drops
lock for M_WAITOK allocation. This will be addressed in separate
commit.

r259663 (glebius):
Move list of ttys handling from the allocating procedures, to the
device creation stage. A device creation can fail, and in that case
an entry already on the list will be freed.

KBI issue pointed out by: kib
Reviewed by: kib (KBI addition)
Approved by: re (kib)

MFC 259016,259019,259049,259071,259102,259110,259129,259130,259178,259179,
259203,259221,259261,259532,259615,259650,259651,259667,259680,259727,
259761,259772,259776,259777,259830,259882,259915,260160,260449,260450,
260688,260888,260953,261269,261547,261551,261552,261553,261585:
Merge the vt(4) driver (newcons) to stable/10.

Approved by: ray

MFC tty fixes, r259549 and r259663

Keep tty_makedev as a function to preserve the KBI on 10-stable
(it is a macro in CURRENT). The changes for this are direct
commits to 10-stable.

r259549 (glebius):
- Rename tty_makedev() into tty_makedevf() and make it capable
to fail and return error.
- Use make_dev_p() in tty_makedevf() instead of make_dev_cred().
- Always pass MAKEDEV_CHECKNAME flag.
- Optionally pass MAKEDEV_REF flag.
- Provide macro for compatibility with old API.

This fixes races with simultaneous creation and desctruction of
ttys, and makes it possible to call tty_makedevf() from device
cloners.

A race in tty_watermarks() still exist, since the latter drops
lock for M_WAITOK allocation. This will be addressed in separate
commit.

r259663 (glebius):
Move list of ttys handling from the allocating procedures, to the
device creation stage. A device creation can fail, and in that case
an entry already on the list will be freed.

KBI issue pointed out by: kib
Reviewed by: kib (KBI addition)
Approved by: re (kib)

MFC 259016,259019,259049,259071,259102,259110,259129,259130,259178,259179,
259203,259221,259261,259532,259615,259650,259651,259667,259680,259727,
259761,259772,259776,259777,259830,259882,259915,260160,260449,260450,
260688,260888,260953,261269,261547,261551,261552,261553,261585:
Merge the vt(4) driver (newcons) to stable/10.

Approved by: ray