TTY: pass flags to alloc_tty_driver

We need to allow drivers that use neither tty_port_install nor
tty_port_register_device to link a tty_port to a tty somehow.  To
avoid a race with open, this has to be performed before
tty_register_device. But currently tty_driver->ports is allocated even
in tty_register_device because we do not know whether this is the PTY
driver. The PTY driver is special here due to an excessive count of
lines it declares to handle. We cannot handle tty_ports there this
way.

To circumvent this, we start passing tty_driver flags to
alloc_tty_driver already and we create tty_alloc_driver for this
purpose. There we can allocate tty_driver->ports and do all the magic
between tty_alloc_driver and tty_register_device. Later we will
introduce tty_port_link_device function for that purpose.

All drivers should eventually switch to this new tty driver allocation
interface.

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