misc: pti, use tty_port_register_device

So now we have enough of tty_ports, so we can signal the TTY layer to
use them by tty_port_register_device.

The upside is that we look like we can introduce tty_port_easy_open
and put it directly as tty_operations->open to drivers doing nothing
in open and using tty_port_register_device. Because the easy open can
obtain a tty_port rather easily from a tty now. Heh, what a nice
by-product.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: J Freyensee <james_p_freyensee@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>