qdev: Don't leak string property value on hot unplug

parse_string() qemu_strdup()s the property value.  It is never freed.
It needs to be freed along with the device.  Otherwise, the value of
scsi-disk property "ver" gets leaked when hot-unplugging the disk, for
instance.

Call new PropertyInfo method free() from qdev_free().  Implement it
for qdev_prop_string.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/hw/qdev.c b/hw/qdev.c
index aa2ce01..29f6e9f 100644
--- a/hw/qdev.c
+++ b/hw/qdev.c
@@ -334,6 +334,7 @@
 void qdev_free(DeviceState *dev)
 {
     BusState *bus;
+    Property *prop;
 
     if (dev->state == DEV_STATE_INITIALIZED) {
         while (dev->num_child_bus) {
@@ -349,6 +350,11 @@
     }
     qemu_unregister_reset(qdev_reset, dev);
     QLIST_REMOVE(dev, sibling);
+    for (prop = dev->info->props; prop && prop->name; prop++) {
+        if (prop->info->free) {
+            prop->info->free(dev, prop);
+        }
+    }
     qemu_free(dev);
 }