write_tiles_in_tg_obus: use fewer bytes for tile sizes
write_tiles_in_tg_obus: use fewer bytes for tile sizes

remux tiles similar to EXT_TILE/large_scale_tile; this is only done for
a single tile group for now to avoid parsing those in the remux call.

BUG=aomedia:1506

Change-Id: Ia21d718e2496e5a2968cec9a48047523af46aed3

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom