virtio-blk: modernize sysfs attribute creation

commit e982c4d0a29b1d61fbe7716a8dcf8984936d6730 upstream.

Use new-style DEVICE_ATTR_RO/DEVICE_ATTR_RW to create the sysfs attributes
and register the disk with default sysfs attribute groups.

Signed-off-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>