Segments can't be larger than the maximum DMA mapping size
supported on the platform. Take that into account when
setting the maximum segment size for a block device.

Cc: stable@vger.kernel.org
Reviewed-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJoerg Roedel <jroedel@suse.de>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>