ses: generate KOBJ_CHANGE on enclosure attach

In support of a /dev/disk/by-slot populated with data from the enclosure
and ses modules udev needs notification when the new interface
files/links are available.  Otherwise, any udev rules specified for the
disk cannot assume that the enclosure topology has settled.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Reviewed-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>