Fix compilation with --disable-everything --enable-parser=vc1.
mpeg12enc: add support for PANSCAN side data in sequence_display_extension

Signed-off-by: Marton Balint <cus@passwd.hu>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
mpeg12enc: add seq_disp_ext option for deciding when to write a sequence_display_extension

Signed-off-by: Marton Balint <cus@passwd.hu>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>