radeonsi: do not kill GS with memory writes

radeonsi: do not kill GS with memory writes

Vertex emits beyond the specified maximum number of vertices are supposed to
have no effect, which is why we used to always kill GS that reached the limit.

However, if the GS also writes to memory (SSBO, atomics, shader images), then
we must keep going and only skip the vertex emit itself.

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Marek Olšák <marek.olsak@amd.com>