For Z cards, use tty helpers for dtr_rts.

If we did the same for Y cards, it will cause a deadlock, because
cyy_dtr_rts takes a lock which we already hold.

Instead, we introduce a Y helper expecting card lock to be held.
It may then be called with set/clear masks from other places.
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>