backport: winsys/amdgpu: Retrieve WC flags from imported buffers.
Otherwise reading from an imported mapped GTT+WC linear texture is painfully slow.
Sadly no radeon winsys implementation, as I don't know a suitable kernel driver operation.
Hit this in vaGetImage with an image imported from minigbm (which we are switching to allocate WC for SCANOUT images).
Cc: email@example.com Reviewed-by: Marek Olšák firstname.lastname@example.org Acked-by: Pierre-Eric Pelloux-Prayer email@example.com Part-of: !4542 (merged) (cherry picked from commit d80fb024)