vapool: self explain video info variables
There's no need of a union in the private structure since GstVideoInfoDmaDrm contains at the beginning the GstVideoInfo. Then, GstVideoInfoDmaDrm can handle both cases (dma and non-dma).
In order to clarify where the info structures comes from, they are renamed to caps_info, that comes from the caps, and alloc_info that comes from the allocator.
Set force_videometa only if downstream doesn't support it .
Spurious asserts and assignations were removed.
cc: @He_Junyan