New QMP command query-cpu-max and HMP command cpu_max

These commands return the maximum number of CPUs supported by the
currently running emulator instance, as defined in its QEMUMachine
struct.

Signed-off-by: Michal Novotny <minovotn@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

qmp-commands.hx

@@ -382,6 +382,28 @@ Example:
 
 Note: CPUs' indexes are obtained with the 'query-cpus' command.
 
+EQMP
+
+    {
+        .name       = "query-cpu-max",
+        .args_type  = "",
+        .mhandler.cmd_new = qmp_marshal_input_query_cpu_max,
+    },
+
+SQMP
+query-cpu-max
+-------------
+
+Get the maximum CPUs supported by the machine being currently
+emulated.
+
+Returns json-int.
+
+Example:
+
+-> { "execute": "query-cpu-max" }
+<- { "return": 255 }
+
 EQMP
 
     {