tty: audit: move some local functions out of tty.h

The functions tty_audit_add_data() and tty_audit_tiocsti() are local to
the tty core code, and do not need to be in a "kernel-wide" header file
so move them to drivers/tty/tty.h

Cc: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20210408125134.3016837-9-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>