It is valid for HEVC; in fact, the ATSC-HEVC spec [1] simply
refers to the relevant H.264 spec.

It is also trivial to implement now: Just move applying AFD
to ff_h2645_sei_to_frame() and stop ignoring AFD when parsing
a HEVC SEI containing it.

A FATE-test for this has been added.

[1]: https://www.atsc.org/atsc-documents/a3412017-video-hevc/Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>