radeonsi: scale the number of shader compiler threads

Instead of spawning all the threads on startup.

This speeds up short lived programs (eg: piglit runs duration is reduced by ±25%),
avoid wasting resources and still make use of multi-threaded capabilities.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16273>
1 file changed