[PATCH] md: initial sysfs support for md

Start using kobjects in mddevs, and provide a couple of simple attributes
(level and disks).  Attributes live in
  /sys/block/mdX/md/attr-name

Signed-off-by: Neil Brown <neilb@suse.de>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>