nir/zink: use sysvals in `nir_create_passthrough_gs`

nir/zink: use sysvals in `nir_create_passthrough_gs`

Previously the passthrough gs shader loaded some values with uniform
loads using sevaral hardcoded values.

This was not flexible for other drivers and started becoming too
unflexible for zink itself.

Use system values instead and use a lowering pass in zink.

Acked-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22667>