radv: Call radv_pipeline_init_scratch per shader

radv: Call radv_pipeline_init_scratch per shader

Compute pipelines only have one shader, which was not handled correctly
in the case of ray tracing pipelines. Adding radv_shader as an argument
allows us to handle the ray tracing prolog. The original loop is inlined
into its only user (radv_pipeline_graphics.c).

Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23812>