Rework slave allocation:
  - separate the tagging support setup from the hostdata setup
  - make the hostdata setup act consistently when the lookup fails
  - make the hostdata setup act consistently when the device is not added
  - set up the queue depth consistently across these scenarios
  - if the block layer mq support is not available, explicitly enable and
    activate the SCSI layer tcq support (and do this at allocation-time so
    that the tags will be available for INQUIRY commands)

Tweak slave configuration so that devices which are masked are also
not attached.
Reviewed-by: NScott Teel <scott.teel@pmcs.com>
Reviewed-by: NKevin Barnett <kevin.barnett@pmcs.com>
Reviewed-by: NTomas Henzl <thenzl@redhat.com>
Reviewed-by: NHannes Reinecke <hare@Suse.de>
Signed-off-by: NWebb Scales <webbnh@hp.com>
Signed-off-by: NDon Brace <don.brace@pmcs.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJames Bottomley <JBottomley@Odin.com>