vfio/nvgrace: Support get_dmabuf_phys

vfio/nvgrace: Support get_dmabuf_phys

Call vfio_pci_core_fill_phys_vec() with the proper physical ranges for the
synthetic BAR 2 and BAR 4 regions. Otherwise use the normal flow based on
the PCI bar.

This demonstrates a DMABUF that follows the region info report to only
allow mapping parts of the region that are mmapable. Since the BAR is
power of two sized and the "CXL" region is just page aligned the there can
be a padding region at the end that is not mmaped or passed into the
DMABUF.

The "CXL" ranges that are remapped into BAR 2 and BAR 4 areas are not PCI
MMIO, they actually run over the CXL-like coherent interconnect and for
the purposes of DMA behave identically to DRAM. We don't try to model this
distinction between true PCI BAR memory that takes a real PCI path and the
"CXL" memory that takes a different path in the p2p framework for now.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Alex Mastro <amastro@fb.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Acked-by: Ankit Agrawal <ankita@nvidia.com>
Reviewed-by: Ankit Agrawal <ankita@nvidia.com>
Link: https://lore.kernel.org/r/20251120-dmabuf-vfio-v9-11-d7f71607f371@nvidia.com
Signed-off-by: Alex Williamson <alex@shazbot.org>