iommu: Stop exporting iommu_map_sg_atomic()

Function iommu_map_sg_atomic() is only referenced in dma-iommu.c, which
can only be built-in, so stop exporting.

Signed-off-by: John Garry <john.garry@huawei.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/1609940111-28563-5-git-send-email-john.garry@huawei.com


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