Handle unsupported bitstream while large-scale-tile=1

This patch follows the previous one to handle large-scale-tile=1
bitstream in decoder by assigning a different fourcc. Also,
modified lightfield example accordingly.

Details:
aomenc/lightfield_encoder: for large scale tile(LST) encoding,
write LST_FOURCC to output bitstream.

aomdec: if input bitstream's fourcc isn't equal to AV1_FOURCC,
decoder fails with unsupported fourcc error message.

lightfield_bitstream_parsing: convert LST bitstream to AV1
bitstream. Set fourcc to AV1_FOURCC and write it to output
bitstream.

BUG=aomedia:2274

Change-Id: Iadc88b0e9804badb8e5d014be0f0796fb2d6ce25

common/video_reader.h

diff --git a/common/video_reader.h b/common/video_reader.h
index 903deae..9ab439e 100644
--- a/common/video_reader.h
+++ b/common/video_reader.h
@@ -50,6 +50,9 @@
 // Fills AvxVideoInfo with information from opened video file.
 const AvxVideoInfo *aom_video_reader_get_info(AvxVideoReader *reader);
 
+// Set fourcc.
+void aom_video_reader_set_fourcc(AvxVideoReader *reader, uint32_t fourcc);
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif