radeonsi: pass at most 3 images and/or shader buffers via user SGPRs for compute

This should slightly decrease shader lifetime.

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5209>

src/gallium/drivers/radeonsi/si_shader_internal.h

@@ -171,6 +171,8 @@ struct si_shader_context {
    /* CS */
    struct ac_arg block_size;
    struct ac_arg cs_user_data;
+   struct ac_arg cs_shaderbuf[3];
+   struct ac_arg cs_image[3];
 
    struct ac_llvm_compiler *compiler;