d3d11decoder: Support DXGI_FORMAT_420_OPAQUE format
See the ffmpeg commit https://github.com/FFmpeg/FFmpeg/commit/8d7fdba7b8670db9dd5023dde6fe3a06674933c4
I tested the DXGI_FORMAT_420_OPAQUE format on Intel platform, then there seems to be no benefit in terms of performance or resources in the desktop environment with d3d11videoprocessor/d3d11videosink. I had a hopeful guess that it could be more h/w friendly memory layout than NV12 but I didn't see any benefit of DXGI_FORMAT_420_OPAQUE format. However, supporting the format may be valuable in terms of extending the coverage of gstd3d11decoder.