avcodec/avdct: Add avcodec_dct_get_class()

This should have been in the initial commit of AVDCT

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/vf_scale: fix log message category

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/vf_spp: support setting dct avoptions from the filter graph string

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