Revert "scsi: default to scsi-mq"

Revert "scsi: default to scsi-mq"

Defaulting to scsi-mq in 4.13-rc has shown various regressions
on setups that we didn't previously consider.  Fixes for them are
in progress, but too invasive to make it in this cycle.  So for
now revert the commit that defaults to blk-mq for SCSI.  For 4.14
we'll plan to try again with these fixes.

This reverts commit 5c279bd9e40624f4ab6e688671026d6005b066fa.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>