iommu: remove iommu_domain_{get,set}_attr

Remove the now unused iommu attr infrastructure.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210401155256.298656-21-hch@lst.de


Signed-off-by: Joerg Roedel <jroedel@suse.de>