gigesimsink: allow compiling with GStreamer < 1.10

IYU2 was added in 1.10, but we'd like to be able to build against 1.2,
so define the pixel type if it doesn't exist.

ext/gigesim/gstgigesim.cpp

@@ -39,6 +39,11 @@
 
 #include "gstgigesim.h"
 
+/* IYU2 was added in GStreamer 1.10, define here if needed */
+#ifndef GST_VIDEO_FORMAT_IYU2
+#define GST_VIDEO_FORMAT_IYU2 63
+#endif
+
 /* GObject prototypes */
 static void gst_gigesimsink_set_property (GObject * object,
     guint property_id, const GValue * value, GParamSpec * pspec);