dmabuf: Move a declaration

We will need to access this struct from the Wayland backend.

gdk/gdkdmabufformats.c

@@ -49,14 +49,6 @@
  * Since: 4.14
  */
 
-struct _GdkDmabufFormats
-{
-  int ref_count;
-
-  gsize n_formats;
-  GdkDmabufFormat *formats;
-};
-
 G_DEFINE_BOXED_TYPE (GdkDmabufFormats, gdk_dmabuf_formats, gdk_dmabuf_formats_ref, gdk_dmabuf_formats_unref)
 
 /**

gdk/gdkdmabufformatsprivate.h

@@ -9,6 +9,14 @@ struct _GdkDmabufFormat
   guint64 modifier;
 };
 
+struct _GdkDmabufFormats
+{
+  int ref_count;
+
+  gsize n_formats;
+  GdkDmabufFormat *formats;
+};
+
 GdkDmabufFormats *      gdk_dmabuf_formats_new                  (GdkDmabufFormat  *formats,
                                                                  gsize             n_formats);