Implement proper wb_valid semantics for CLIC pointer fetches and multi operation instructions

Created by: silabs-oysteink

Currently, a CLIC pointer that arrives in WB will not signal wb_valid, and RVFI is not notified of the pointer. Similarly, split LSU accesses only signal wb_valid for the last operation, not the first.

Wb_valid should be set for all cycles where a valid instruction or part of an instruction is done in WB (similar to id_valid and ex_valid for instance). RVFI would need to adapt to this by for instance checking the 'last' bit inside it's pipeline model.