configure: update dependencies for vf_spp

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/img2dec: increase probe buffer to 2k

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/img2dec: improve bmp probe

fix probetest failure

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