we are starting to split gendisks - now we can do that.  Done for
ide, sd, pd, hd and mfm

It's in transit - what we are aiming at is getting ->nr_real to 1 for
all gendisks.  Once that will be done we will be able to simplify a lot
stuff and remove ad-hackery.  First thing that will happen after that
is death of ->nr_real, obviouslye.  Then we
	(a) will merge ->major and ->first_minor into ->dev
	(b) strip one level of indirection from  ->driverfs_dev_arr, ->de_arr
and ->flags - they turn into single-element arrays and we will simply pull
the (only) element into struct gendisk.  Kills a lot of ad-hackery in splitup
code (fewer things to allocate).
	(c) replace ->major_name with ->disk_name; kills most of the crap in
disk_name(9) - it only has to care about adding partition number to the name.