iommu: remove the put_resv_regions method

All drivers that implement get_resv_regions just use
generic_put_resv_regions to implement the put side.  Remove the
indirections and document the allocations constraints.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20220708080616.238833-4-hch@lst.de
Signed-off-by: Joerg Roedel <jroedel@suse.de>