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 b4f640d3509954e59cf439498d724dc404328379.

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>