scsi: check that busses support the DMA API before setting dma parameters

We'll start throwing warnings soon when dma_set_seg_boundary and
dma_set_max_seg_size are called on devices for buses that don't fully
support the DMA API.  Prepare for that by making the calls in the SCSI
midlayer conditional.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>