radv: allocate only 1 GDS OA counter for gfx10 NGG streamout

radv: allocate only 1 GDS OA counter for gfx10 NGG streamout

It works with just one counter.

This mitigates https://gitlab.freedesktop.org/drm/amd/-/issues/2902
quite a lot when you run dEQP-VK.transform_feedback.* in parallel on
more than 16 threads with RDNA3.

For example, on my GPU the kernel reports 16 GDS OA counters which means
that if you run VKCTS with 16 threads (ie. 16 Vulkan devices are
created) it's fine. Otherwise, the kernel might report ENOMEM.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25619>