QMP: Add query-hotpluggable-cpus

It will allow mgmt to query present and hotpluggable CPU objects,
it is required from a target platform that wishes to support command
to implement and set MachineClass.query_hotpluggable_cpus callback,
which will return a list of possible CPU objects with options that
would be needed for hotplugging possible CPU objects.

There are:
'type': 'str' - QOM CPU object type for usage with device_add
'vcpus-count': 'int' - number of logical VCPU threads per
                        CPU object (mgmt needs to know)

and a set of optional fields that are to used for hotplugging a CPU
objects and would allows mgmt tools to know what/where it could be
hotplugged;
[node],[socket],[core],[thread]

For present CPUs there is a 'qom-path' field which would allow mgmt to
inspect whatever object/abstraction the target platform considers
as CPU object.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
diff --git a/monitor.c b/monitor.c
index a27e115..a5d054b 100644
--- a/monitor.c
+++ b/monitor.c
@@ -4273,3 +4273,16 @@
     return NULL;
 }
 #endif
+
+HotpluggableCPUList *qmp_query_hotpluggable_cpus(Error **errp)
+{
+    MachineState *ms = MACHINE(qdev_get_machine());
+    MachineClass *mc = MACHINE_GET_CLASS(ms);
+
+    if (!mc->query_hotpluggable_cpus) {
+        error_setg(errp, QERR_FEATURE_DISABLED, "query-hotpluggable-cpus");
+        return NULL;
+    }
+
+    return mc->query_hotpluggable_cpus(ms);
+}