Merge commit '881477c7'

* commit '881477c7':
  swscale: Add the GBRAP12 output
  Add GBRAP12 pixel format support
  swscale: Enable GBRP12 output
  swscale: x86: Add some forgotten 12-bit planar YUV cases
  swscale: Add input support for 12-bit formats

This merge is noop, these commits are recrafted cherry-picks from
FFmpeg.
Merged-by: Clément Bœsch <u@pkh.me>