radeonsi: pre-generate shader logs for ddebug

radeonsi: pre-generate shader logs for ddebug

This cuts down the overhead of si_dump_shader when ddebug is capturing
shader logs, which is done for every draw call unconditionally (that's
quite a lot of work for a draw call).

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>