iommu/arm-smmu: Fix atomic domain handling

Query if a domain is atomic or not after initializing the
domain, as opposed to before, when the domain properties
have not been finalized.

Change-Id: Ib2f05156268a16cccb410e263de957d9eb2070ae
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>