Propagated is_decoding signal to the APU_DISPATCHER to mask read and write dependency

Created by: OttG

FIX

Propagate the is_decoding signal from the controller to the apu_dispatcher to mask read and write dependency. There was a case that, when the fetch_valid signal in the if_stage was 0, the instruction in the decode_stage would not advance but that same instruction would go to the ex_stage. This would cause a false read dependency with the currently executed instruction and the instruction it self (since the instruction in the id_stage and ex_stage was the same). Masking it with the is_decoding signal fixes this performance bug avoiding an extra stall when this happened.