vfio/nvgrace-gpu: Expose the blackwell device PF BAR1 to the VM

There is a HW defect on Grace Hopper (GH) to support the
Multi-Instance GPU (MIG) feature [1] that necessiated the presence
of a 1G region carved out from the device memory and mapped as
uncached. The 1G region is shown as a fake BAR (comprising region 2 and 3)
to workaround the issue.

The Grace Blackwell systems (GB) differ from GH systems in the following
aspects:
1. The aforementioned HW defect is fixed on GB systems.
2. There is a usable BAR1 (region 2 and 3) on GB systems for the
GPUdirect RDMA feature [2].

This patch accommodate those GB changes by showing the 64b physical
device BAR1 (region2 and 3) to the VM instead of the fake one. This
takes care of both the differences.

Moreover, the entire device memory is exposed on GB as cacheable to
the VM as there is no carveout required.

Link: https://www.nvidia.com/en-in/technologies/multi-instance-gpu/ [1]
Link: https://docs.nvidia.com/cuda/gpudirect-rdma/ [2]

Cc: Kevin Tian <kevin.tian@intel.com>
CC: Jason Gunthorpe <jgg@nvidia.com>
Suggested-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
Link: https://lore.kernel.org/r/20250124183102.3976-3-ankita@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

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