iommu/tegra: Do not use struct page as the handle for pts

Instead use the virtual address and dma_map_single() like as->pd
uses. Introduce a small struct tegra_pt instead of void * to have some
clarity what is using this API and add compile safety during the
conversion.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/2-v4-c8663abbb606+3f7-iommu_pages_jgg@nvidia.com


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