virtio_console: support console resizing

this patch uses the new hvc callback hvc_resize to set the window size
which allows to change the tty size of hvc_console via a hvc_resize
function.

I have added a new feature bit VIRTIO_CONSOLE_F_SIZE. The driver will
change the window size on tty open and via the config_changed callback
of the transport. Currently lguest and kvm_s390 have not implemented this
callback, but the callback can be implemented at a later point in time.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/char/hvc_console.c

@@ -695,6 +695,7 @@ void hvc_resize(struct hvc_struct *hp, struct winsize ws)
 	hp->ws = ws;
 	schedule_work(&hp->tty_resize);
 }
+EXPORT_SYMBOL_GPL(hvc_resize);
 
 /*
  * This kthread is either polling or interrupt driven.  This is determined by