Reorder nut specific codec tags and add a comment for marking them as

Reorder nut specific codec tags and add a comment for marking them as
such.

Also put the [3][0][0][0] codec tag, mapped to rgb565le, in a special
section. It needs to be specified *after* the nut RGB[16] codec tag,
otherwise it will be used by default when encoding normal non-flipped
rgb565le, and will be decoded like a flipped format (see
rawdec.c:raw_init_decoder()).

Originally committed as revision 23075 to svn://svn.ffmpeg.org/ffmpeg/trunk