[SCSI] ses: add subenclosure support

There have been many complaints that an enclosure with subenclosures
isn't attached to by the ses driver.   Until now, though, no-one had
been willing to provide access to one.

Subenclosures are added simply by flattening the tree (i.e. all
subenclosure devices show up under the one main device).  This may have
consequences if the naming is only unique per subenclosure, but that's a
bug for another day.  The tested array had no page 7, so no device
naming at all.  It also only had the disk devices on one of its
subenclosures (all the others had power, fans, temperature and various
sensors), so testing of this is fairly rudimentary.

Signed-off-by: James Bottomley <James.Bottomley@suse.de>