iommu/io-pgtable-arm: Remove iommu_dev==NULL special case

iommu/io-pgtable-arm: Remove iommu_dev==NULL special case

The special case to allow iommu_dev==NULL in __arm_lpae_alloc_pages() is
confusing to static checkers (and possibly readers in general), since
it's not obvious that that is only intended for the selftests. However
it only serves to get around the dev_to_node() call, and we can easily
fake up enough to make that work anyway, so let's simply remove this
consideration from the normal flow and punt the responsibility over to
the test harness itself.

Reported-by: Rustam Subkhankulov <subkhankulov@ispras.ru>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/e2095eeda305071cb56c2cb8ac8a82dc3bd4dcab.1660580155.git.robin.murphy@arm.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>