scsi: replace "mq" with "first_chunk" in SG functions

Parameter "bool mq" is block driver specific.
Change it to "first_chunk" to make it more generic.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lin <ming.l@ssi.samsung.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>