iommu: Remove apply_resv_region

The apply_resv_region callback in iommu_ops was introduced to reserve an
IOVA range in the given DMA domain when the IOMMU driver manages the IOVA
by itself. As all drivers converted to use dma-iommu in the core, there's
no driver using this anymore. Remove it to avoid dead code.

Suggested-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20220216025249.3459465-6-baolu.lu@linux.intel.com


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