Merge commit '3399a26d'

* commit '3399a26d':
  nvenc: allow setting the number of slices
  nvenc: De-compensate aspect ratio compensation of DVD-like content.
  nvenc: list the major contributors in the copyright header
  configure: Don't require nonfree for nvenc
  nvenc: drop the hard dependency on CUDA
  nvenc: only support HW frames when CUDA is enabled
  nvenc: write the VUI signal properties for HEVC
  nvenc: only write the VUI signal type fields if they are set
  nvenc: Generate bufferingPeriod/pictureTiming SEI
  nvenc: Delay frame output to increase encoding speed
  nvenc: add support for lossless encoding
  nvenc: Generate AUD NAL units for better compatiblity
  nvenc: fix the rc option definitions

All these commits are noop as requested by Timo Rothenpieler.

<BtbN> andrey_turkin, ubitux, yeah, I like the current state of nvenc in
ffmpeg, I think most remaining differences should be merged on the libav
side of things. At least I'm not aware of anything that's missing in
ffmpeg.
Merged-by: Clément Bœsch <u@pkh.me>