radv: Don't toggle PC oversubscription for NGG culling.

We are going to add this directly to the pipeline.
If a pipeline has such a shader, NGG culling is turned on
most of the time, so it's not useful to toggle this setting.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11905>