decode: clear op_mtspr_o on decode_bubble
cappuccino/execute_ctrl: remove nop on rfe

The situation this was needed for doesn't exist anymore,
the pipeline_flush below does the same job.
cappuccino/ctrl: input/output line-up fix
cappuccino/ctrl: remove unused execute_op_mfspr signal
cappuccino/ctrl: use existing ctr_op_mfspr/mtspr signals

instead of decoding them again in control stage