d3d12: NV12 resource support
This is the first 4 patches from !13533 (closed). Since these shouldn't be contentious, splitting them out to land ahead of figuring out how to deal with YV12 emulation - leaving !13533 (closed) for that since it has some discussion already started.
These patches add support for importing NV12 resources using Mesa's lowering, where we see a request to open 2 planes, one with R8 and the other with R8G8. It also supports opening/creating resources of NV12 format without the lowering, where it's one resource, to be used for video.
/cc @sivileri