Instead make the global iommu_dma_strict paramete in iommu.c canonical by
exporting helpers to get and set it and use those directly in the drivers.

This make sure that the iommu.strict parameter also works for the AMD and
Intel IOMMU drivers on x86.  As those default to lazy flushing a new
IOMMU_CMD_LINE_STRICT is used to turn the value into a tristate to
represent the default if not overriden by an explicit parameter.

[ported on top of the other iommu_attr changes and added a few small
 missing bits]

Signed-off-by: Robin Murphy <robin.murphy@arm.com>.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210401155256.298656-19-hch@lst.deSigned-off-by: NJoerg Roedel <jroedel@suse.de>