mcause.minhv clear from WB stage

Created by: silabs-oysteink

Moved clearing of mcause.minhv for successful pointer fetches from ID to WB. This aligns with other state changes that also happens from WB. Should fix issue where a killed mret could still lead to clearing of mcause.minhv.

Remoted separate single_step_pending flag for pointer fetches, as single step now can use the wb_valid for the pointer to signal step entry.

Signed-off-by: Oystein Knauserud Oystein.Knauserud@silabs.com