Move AVCodecTag from riff.h into internal.h.

Patch by Francesco Lavra, francescolavra interfree it

Originally committed as revision 23250 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/internal.h

@@ -24,6 +24,11 @@
 #include <stdint.h>
 #include "avformat.h"
 
+typedef struct AVCodecTag {
+    enum CodecID id;
+    unsigned int tag;
+} AVCodecTag;
+
 void ff_dynarray_add(intptr_t **tab_ptr, int *nb_ptr, intptr_t elem);
 
 #ifdef __GNUC__