Mark mutable static data const where appropriate.

avprobe.c

avserver.c

libavcodec/aacdec.c

libavcodec/libvpxenc.c

libavcodec/libxvid_rc.c

libavfilter/vf_boxblur.c

libavfilter/vf_crop.c

libavfilter/vf_drawtext.c

libavfilter/vf_lut.c

libavfilter/vf_overlay.c

libavfilter/vf_pad.c

libavfilter/vf_scale.c

libavfilter/vf_select.c

libavfilter/vf_setpts.c

libavfilter/vf_settb.c

libavfilter/vsrc_nullsrc.c

libavformat/matroskadec.c

libavutil/eval.c