iommu: Implement of_iommu_get_resv_regions()

iommu: Implement of_iommu_get_resv_regions()

This is an implementation that IOMMU drivers can use to obtain reserved
memory regions from a device tree node. It uses the reserved-memory DT
bindings to find the regions associated with a given device. If these
regions are marked accordingly, identity mappings will be created for
them in the IOMMU domain that the devices will be attached to.

Cc: Frank Rowand <frowand.list@gmail.com>
Cc: devicetree@vger.kernel.org
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20230120174251.4004100-4-thierry.reding@gmail.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>