paride initialization cleanup

Hi Jens,

the paride drivers currently have a major Linux 1.x-style mess for
initializing the gendisks.  This series refactors them to be modular
and self-contained in preparation of error handling for add_disk.

Diffstat:
 pcd.c |  298 +++++++++++++++++++++++++++++-------------------------------------
 pd.c  |  142 +++++++++++++++----------------
 pf.c  |  223 +++++++++++++++++++++----------------------------
 3 files changed, 303 insertions(+), 360 deletions(-)