blk-mq does not support runtime pm, so disable blk-mq support for now.

Fixes: d5038a13 ("scsi: core: switch to scsi-mq by default")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>