block: untangle request_queue refcounting from sysfs

block: untangle request_queue refcounting from sysfs

The kobject embedded into the request_queue is used for the queue
directory in sysfs, but that is a child of the gendisks directory and is
intimately tied to it.  Move this kobject to the gendisk and use a
refcount_t in the request_queue for the actual request_queue refcounting
that is completely unrelated to the device model.

Signed-off-by: Christoph Hellwig <hch@lst.de>