- name_to_kdev_t() turned into name_to_dev_t(), callers updated.
 - table of names is gone, we use driverfs instead.

 - root name is converted to dev_t only at prepare_namespace() time - we
   use to do it in setup and we need it after driver initialization.  So
   setup only stores the root name and leaves the work to
   prepare_namespace().

 - disk names for rd and cm206 changed to match the old behaviour of
   root= parser: ramdisks have ram<n> in ->disk_name now (instead of
   rd<n>) and cm206 - cm206cd (instead of cm206).