virtio_pmem: populate numa information

Compute the numa information for a virtio_pmem device from the memory
range of the device. Previously, the target_node was always 0 since
the ndr_desc.target_node field was never explicitly set. The code for
computing the numa node is taken from cxl_pmem_region_probe in
drivers/cxl/pmem.c.

Signed-off-by: Michael Sammler <sammler@google.com>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta@amd.com>
Tested-by: Mina Almasry <almasrymina@google.com>
Message-Id: <20221115214036.1571015-1-sammler@google.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>