avcodec: fourcc: add av1 mapping

Needed to mux AV1 using libavformat's IVF muxer.
IVF muxing for AV1 was added to ffmpeg in
commit e8f0a463b0d27a4d74c0d9f1857e72a8033d1069.

modules/codec/avcodec/fourcc.c

@@ -223,6 +223,9 @@ static const struct vlc_avcodec_fourcc video_codecs[] =
     { VLC_CODEC_CLLC, AV_CODEC_ID_CLLC },
     { VLC_CODEC_MSS2, AV_CODEC_ID_MSS2 },
     { VLC_CODEC_VP9, AV_CODEC_ID_VP9 },
+#if LIBAVCODEC_VERSION_CHECK( 57, 26, 0, 83, 101 )
+    { VLC_CODEC_AV1, AV_CODEC_ID_AV1 },
+#endif
     { VLC_CODEC_ICOD, AV_CODEC_ID_AIC },
     /* AV_CODEC_ID_ESCAPE130 */
     { VLC_CODEC_G2M4, AV_CODEC_ID_G2M },