scsi: add a no_highmem flag to struct Scsi_Host

scsi: add a no_highmem flag to struct Scsi_Host

While we really should be killing the block layer bounce buffering ASAP,
I even more urgently need to stop the drivers to fiddle with the limits
from ->slave_configure.  Add a no_highmem flag to the Scsi_Host to
centralize this setting and switch the remaining four drivers that use
block layer bounce buffering to it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>