hw/acpi/nvdimm: add a helper to augment SRAT generation

hw/acpi/nvdimm: add a helper to augment SRAT generation

NVDIMMs can belong to their own proximity domains, as described by the
NFIT. In such cases, the SRAT needs to have Memory Affinity structures
in the SRAT for these NVDIMMs, otherwise Linux doesn't populate node
data structures properly during NUMA initialization. See the following
for an example failure case.

https://lore.kernel.org/linux-nvdimm/20200416225438.15208-1-vishal.l.verma@intel.com/

Introduce a new helper, nvdimm_build_srat(), and call it for both the
i386 and arm versions of 'build_srat()' to augment the SRAT with
memory affinity information for NVDIMMs.

The relevant command line options to exercise this are below. Nodes 0-1
contain CPUs and regular memory, and nodes 2-3 are the NVDIMM address
space.

    -object memory-backend-ram,id=mem0,size=2048M
    -numa node,nodeid=0,memdev=mem0,
    -numa cpu,node-id=0,socket-id=0
    -object memory-backend-ram,id=mem1,size=2048M
    -numa node,nodeid=1,memdev=mem1,
    -numa cpu,node-id=1,socket-id=1
    -numa node,nodeid=2,
    -object memory-backend-file,id=nvmem0,share,mem-path=nvdimm-0,size=16384M,align=1G
    -device nvdimm,memdev=nvmem0,id=nv0,label-size=2M,node=2
    -numa node,nodeid=3,
    -object memory-backend-file,id=nvmem1,share,mem-path=nvdimm-1,size=16384M,align=1G
    -device nvdimm,memdev=nvmem1,id=nv1,label-size=2M,node=3

Cc: Jingqi Liu <jingqi.liu@intel.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Jingqi Liu <jingqi.liu@intel.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Message-Id: <20200606000911.9896-3-vishal.l.verma@intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>