Support detecting and demuxing EIA-608 subtitles in mov.

The format is slightly proprietary.
DVDs use a format of
code byte (0x00, 0x01, 0xfe or 0xff), two data bytes
MOV uses instead
cdat/cdt2 atom, two data bytes
Auto-detecting and supporting both in one decoder is trivial,
so a single codec ID is used.

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>