memory/iommu: QOM'fy IOMMU MemoryRegion

memory/iommu: QOM'fy IOMMU MemoryRegion

This defines new QOM object - IOMMUMemoryRegion - with MemoryRegion
as a parent.

This moves IOMMU-related fields from MR to IOMMU MR. However to avoid
dymanic QOM casting in fast path (address_space_translate, etc),
this adds an @is_iommu boolean flag to MR and provides new helper to
do simple cast to IOMMU MR - memory_region_get_iommu. The flag
is set in the instance init callback. This defines
memory_region_is_iommu as memory_region_get_iommu()!=NULL.

This switches MemoryRegion to IOMMUMemoryRegion in most places except
the ones where MemoryRegion may be an alias.

Signed-off-by: Alexey Kardashevskiy <[email protected]>
Reviewed-by: David Gibson <[email protected]>
Message-Id: <20170711035620[email protected]>
Acked-by: Cornelia Huck <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>