TTY: vt, add ->install

We need to initialize the console only on the first open. This is
usually what is done in the ->install hook. vt used to do this in
->open. Now we move it to ->install and use newly added helper for
install: tty_port_install. It ensures tty->port to be set properly.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>