pc: ACPI BIOS: use highest NUMA node for hotplug mem hole SRAT entry

pc: ACPI BIOS: use highest NUMA node for hotplug mem hole SRAT entry

For reasons unknown, Windows won't online all memory, both at command
line and hot-plugged later, unless the hotplug mem hole SRAT entry
specifies a node greater than or equal to the ones where memory is
added.

Using the highest node on the machine makes recent versions of Windows
happy.

With this example command line:
  ... \
  -m 1024,slots=4,maxmem=32G \
  -numa node,nodeid=0 \
  -numa node,nodeid=1 \
  -numa node,nodeid=2 \
  -numa node,nodeid=3 \
  -object memory-backend-ram,size=1G,id=mem-mem1 \
  -device pc-dimm,id=dimm-mem1,memdev=mem-mem1,node=1

Windows reports a total of 1G of RAM without this commit and the expected
2G with this commit.

Signed-off-by: Ladi Prosek <lprosek@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>