emulators/vice: unbreak with ffmpeg 4.0

ffmpegdrv.c:363:34: error: use of undeclared identifier 'CODEC_CAP_VARIABLE_FRAME_SIZE'

if (c->codec->capabilities & CODEC_CAP_VARIABLE_FRAME_SIZE) {
                             ^

ffmpegdrv.c:457:21: error: use of undeclared identifier 'CODEC_FLAG_GLOBAL_HEADER'

c->flags |= CODEC_FLAG_GLOBAL_HEADER;
            ^

ffmpegdrv.c:790:21: error: use of undeclared identifier 'CODEC_FLAG_GLOBAL_HEADER'

c->flags |= CODEC_FLAG_GLOBAL_HEADER;
            ^

ffmpegdrv.c:970:40: error: use of undeclared identifier 'AVFMT_RAWPICTURE'

if (ffmpegdrv_oc->oformat->flags & AVFMT_RAWPICTURE) {
                                   ^

PR: 227726