tty: move some tty-only functions to drivers/tty/tty.h

stable inclusion
from stable-v5.10.180
commit 57b510c7d37717784a5c082c7ec66baecfe6dfff
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8FC2O

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=57b510c7d37717784a5c082c7ec66baecfe6dfff

--------------------------------

[ Upstream commit 9f72cab1 ]

The flow change and restricted_tty_write() logic is internal to the tty
core only, so move it out of the include/linux/tty.h file.

Cc: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20210408125134.3016837-12-gregkh@linuxfoundation.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: 094fb49a ("tty: Prevent writing chars during tcsetattr TCSADRAIN/FLUSH")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>