PCI/P2PDMA: Remove the DMA_VIRT_OPS hacks

Now that all users of dma_virt_ops are gone we can remove the workaround
for it in the PCI peer to peer code.

Link: https://lore.kernel.org/r/20201106181941.1878556-9-hch@lst.de


Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>