Documentation: move tty to driver-api

Based on discussion starting as 87mthw2o93.fsf@meer.lwn.net, let's move
the tty documentation to driver-api. It's more appropriate there.

Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220411110143.10019-2-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/driver-api/tty/tty_struct.rst

@@ -0,0 +1,81 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==========
+TTY Struct
+==========
+
+.. contents:: :local:
+
+struct tty_struct is allocated by the TTY layer upon the first open of the TTY
+device and released after the last close. The TTY layer passes this structure
+to most of struct tty_operation's hooks. Members of tty_struct are documented
+in `TTY Struct Reference`_ at the bottom.
+
+Initialization
+==============
+
+.. kernel-doc:: drivers/tty/tty_io.c
+   :identifiers: tty_init_termios
+
+Name
+====
+
+.. kernel-doc:: drivers/tty/tty_io.c
+   :identifiers: tty_name
+
+Reference counting
+==================
+
+.. kernel-doc:: include/linux/tty.h
+   :identifiers: tty_kref_get
+
+.. kernel-doc:: drivers/tty/tty_io.c
+   :identifiers: tty_kref_put
+
+Install
+=======
+
+.. kernel-doc:: drivers/tty/tty_io.c
+   :identifiers: tty_standard_install
+
+Read & Write
+============
+
+.. kernel-doc:: drivers/tty/tty_io.c
+   :identifiers: tty_put_char
+
+Start & Stop
+============
+
+.. kernel-doc:: drivers/tty/tty_io.c
+   :identifiers: start_tty stop_tty
+
+Wakeup
+======
+
+.. kernel-doc:: drivers/tty/tty_io.c
+   :identifiers: tty_wakeup
+
+Hangup
+======
+
+.. kernel-doc:: drivers/tty/tty_io.c
+   :identifiers: tty_hangup tty_vhangup tty_hung_up_p
+
+Misc
+====
+
+.. kernel-doc:: drivers/tty/tty_io.c
+   :identifiers: tty_do_resize
+
+TTY Struct Flags
+================
+
+.. kernel-doc:: include/linux/tty.h
+   :doc: TTY Struct Flags
+
+TTY Struct Reference
+====================
+
+.. kernel-doc:: include/linux/tty.h
+   :identifiers: tty_struct