memory: Introduce memory_region_iommu_set_iova_ranges

This helper will allow to convey information about valid
IOVA ranges to virtual IOMMUS.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: "Michael S. Tsirkin" <mst@redhat.com>
[ clg: fixes in memory_region_iommu_set_iova_ranges() and
       iommu_set_iova_ranges() documentation ]
Signed-off-by: Cédric Le Goater <clg@redhat.com>