iommu/arm-smmu: Make use of phandle iterators in device-tree parsing

Remove the usage of of_parse_phandle_with_args() and replace
it by the phandle-iterator implementation so that we can
parse out all of the potentially present 128 stream-ids.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>