iommu/iova: Squash entry_dtor abstraction

All flush queues are driven by iommu-dma now, so there is no need to
abstract entry_dtor or its data any more. Squash the now-canonical
implementation directly into the IOVA code to get it out of the way.

Reviewed-by: John Garry <john.garry@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/2260f8de00ab5e0f9d2a1cf8978e6ae7cd4f182c.1639753638.git.robin.murphy@arm.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>