radeonsi: remove indirection when loading position at the end for NGG culling

If we store the position into LDS after we know the new thread ID,
we don't need to remember the old thread ID.

The culling code only needs W, X/W, Y/W, so we have to keep those.

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7172>
5 files changed