qemu: add virQEMUCapsSupportsVmport

The vmport machine argument works with pc machine kind, not with xen for
example.

src/qemu/qemu_capabilities.c

@@ -3724,6 +3724,19 @@ virQEMUCapsSupportsChardev(virDomainDefPtr def,
 }
 
 
+bool
+virQEMUCapsSupportsVmport(virQEMUCapsPtr qemuCaps,
+                          const virDomainDef *def)
+{
+    if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_MACHINE_VMPORT_OPT))
+        return false;
+
+    return qemuDomainMachineIsI440FX(def) ||
+        qemuDomainMachineIsQ35(def) ||
+        STREQ(def->os.machine, "isapc");
+}
+
+
 bool
 virQEMUCapsIsMachineSupported(virQEMUCapsPtr qemuCaps,
                               const char *canonical_machine)

src/qemu/qemu_capabilities.h

@@ -263,6 +263,9 @@ bool virQEMUCapsGet(virQEMUCapsPtr qemuCaps,
 bool virQEMUCapsHasPCIMultiBus(virQEMUCapsPtr qemuCaps,
                                virDomainDefPtr def);
 
+bool virQEMUCapsSupportsVmport(virQEMUCapsPtr qemuCaps,
+                               const virDomainDef *def);
+
 char *virQEMUCapsFlagsString(virQEMUCapsPtr qemuCaps);
 
 const char *virQEMUCapsGetBinary(virQEMUCapsPtr qemuCaps);