radeonsi: only emit compute shader state when switching shaders

radeonsi: only emit compute shader state when switching shaders

v2: - Do check if anything changed earlier
    - Use emitted_program instead of emitted_bo to prevent
      shaders with shader->bo = NULL confusing the check
    - Use radeon_set_sh_reg*

Signed-off-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>