This finishes QOM'fication of IOMMUMemoryRegion by introducing
a IOMMUMemoryRegionClass. This also provides a fastpath analog for
IOMMU_MEMORY_REGION_GET_CLASS().

This makes IOMMUMemoryRegion an abstract class.
Signed-off-by: NAlexey Kardashevskiy <aik@ozlabs.ru>
Message-Id: <20170711035620.4232-3-aik@ozlabs.ru>
Acked-by: NCornelia Huck <cohuck@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>