avformat/matroskadec: support SVQ3 as generated by mkvtoolnix-6.6.0

Fixes part of Ticket3256

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/matroskadec: support QDM2 as generated by mkvtoolnix-6.7.0

Fixes part of Ticket3256

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>