qapi/qnull: Add own header

Backports commit 84be629d5545b5ccc5bff2824e4288677e27de9c from qemu

qemu/include/qapi/qmp/qdict.h

@@ -15,7 +15,6 @@
 
 #include "qapi/qmp/qobject.h"
 #include "qapi/qmp/qlist.h"
-#include "qapi/qmp/qnum.h"
 #include "qemu/queue.h"
 #include "unicorn/platform.h"
 

qemu/include/qapi/qmp/qlist.h

@@ -14,7 +14,6 @@
 #define QLIST_H
 
 #include "qapi/qmp/qobject.h"
-#include "qapi/qmp/qnum.h"
 #include "qemu/queue.h"
 
 typedef struct QListEntry {

qemu/include/qapi/qmp/qnull.h

@@ -0,0 +1,30 @@
+/*
+ * QNull
+ *
+ * Copyright (C) 2015 Red Hat, Inc.
+ *
+ * Authors:
+ *  Markus Armbruster <armbru@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.1
+ * or later.  See the COPYING.LIB file in the top-level directory.
+ */
+
+#ifndef QNULL_H
+#define QNULL_H
+
+#include "qapi/qmp/qobject.h"
+
+struct QNull {
+    QObject base;
+};
+
+extern QNull qnull_;
+
+static inline QNull *qnull(void)
+{
+    QINCREF(&qnull_);
+    return &qnull_;
+}
+
+#endif /* QNULL_H */

qemu/include/qapi/qmp/qobject.h

@@ -99,16 +99,4 @@ static inline QType qobject_type(const QObject *obj)
     return obj->type;
 }
 
-struct QNull {
-    QObject base;
-};
-
-extern QNull qnull_;
-
-static inline QNull *qnull(void)
-{
-    QINCREF(&qnull_);
-    return &qnull_;
-}
-
 #endif /* QOBJECT_H */

qemu/qapi/qapi-clone-visitor.c

@@ -12,6 +12,7 @@
 #include "qapi/clone-visitor.h"
 #include "qapi/visitor-impl.h"
 #include "qapi/error.h"
+#include "qapi/qmp/qnull.h"
 
 struct QapiCloneVisitor {
     Visitor visitor;

qemu/qapi/string-input-visitor.c

@@ -16,6 +16,7 @@
 #include "qapi/string-input-visitor.h"
 #include "qapi/visitor-impl.h"
 #include "qapi/qmp/qerror.h"
+#include "qapi/qmp/qnull.h"
 #include "qemu/queue.h"
 #include "qemu/range.h"
 #include <stdlib.h>	// strtoll

qemu/qobject/qnull.c

@@ -11,7 +11,7 @@
  */
 
 #include "qemu-common.h"
-#include "qapi/qmp/qobject.h"
+#include "qapi/qmp/qnull.h"
 
 QNull qnull_ = {
     {