tty/serial: lay the foundations for the next set of reworks

- Stop drivers calling their own flush method indirectly, it obfuscates code
  and it will change soon anyway

- A few more lock_kernel paths temporarily needed in some driver internal
  waiting code

- Remove private put_char method that does a write call for one char - we
  have that anyway

- Most but not yet all of the termios copy under lock fixing (some has other
  dependencies to follow)

- Note a few locking bugs in drivers found in the process

- Kill remaining [ab]users of TIOCG/SSOFTCAR in the driver, these must go to
  fix the termios locking

Signed-off-by: Alan Cox <alan@redhat.com>
Cc: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/generic_serial.c

@@ -586,8 +586,7 @@ void gs_close(struct tty_struct * tty, struct file * filp)
 
 	port->flags &= ~GS_ACTIVE;
 
-	if (tty->driver->flush_buffer)
-		tty->driver->flush_buffer(tty);
+	gs_flush_buffer(tty);
 
 	tty_ldisc_flush(tty);
 	tty->closing = 0;