lavfi/dctdnoiz: move DC normalization out of loops.

Make code slightly faster, simpler, clearer.

The filter is still slow as hell, and that change won't cause any
visible performance improvement (it still takes more than one minute to
process a single 1080p frame on a Core 2 here).
libtwolame: add forgotten calls

Signed-off-by: Paul B Mahol <onemda@gmail.com>
j2k: merge cosmetics and non functional changes from jpeg2000

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