xen/arm: smmuv1: Add a stream map entry iterator

xen/arm: smmuv1: Add a stream map entry iterator

Backport commit d3097e39302083d58922a3d1032d7d59a63d263d
"iommu/arm-smmu: Add a stream map entry iterator" from the Linux kernel.

This patch is the preparatory work to fix the stream match conflict
when two devices have the same stream-id.

Original commit message:
    iommu/arm-smmu: Add a stream map entry iterator

    We iterate over the SMEs associated with a master config quite a lot in
    various places, and are about to do so even more. Let's wrap the idiom
    in a handy iterator macro before the repetition gets out of hand.

    Tested-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
    Signed-off-by: Robin Murphy <robin.murphy@arm.com>
    Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Rahul Singh <rahul.singh@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
Acked-by: Julien Grall <jgrall@amazon.com>