softpipe: count CS invocations for pipeline stats queries.

Part of fixing KHR-GL33.pipeline_statistics_query_tests_ARB.
  functional_compute_shader_invocations

(also requires a test bugfix:
https://gitlab.khronos.org/Tracker/vk-gl-cts/-/issues/2694).

Fixes: e749c30cebe0 ("softpipe: add support for compute shaders. (v2)")
Reviewed-by: Gert Wollny <gert.wollny@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8065>
(cherry picked from commit 5dd5fb1926c72c97571ddcb5f6c696766e7c9abc)
3 files changed