1) Replace is_read_only with bdev_read_only. The last user of is_read_only
   is gone...
2) Remove alloc & free of the label array in dasd_genhd. This is needed for
   the label array extension but this is a patch of its own.
3) Maintain the old behaviour of /proc/dasd/devices. Its is possible again
   to use "add <devno>" instead of "add device <devno>" or "add range=<devno>".