hevc: add partial support for interlaced(cherry picked from commit 44b592ae6d323445c076ef3ec966ebf9daa8bccf)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
libavfilter/decimate: Add pts of first frame to all frames.

Fixes ticket #3019

Reviewed-by: Clément Bœsch