acpi: cpuhp: add cpu._OST handling

it adds HW and AML parts for CPU_Device._OST method
handling to allow OSPM reports status of hot-(un)plug
operation.
And extends QMP command query-acpi-ospm-status to report
CPU's OST info along with already reported PC-DIMM devices.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>