For offline traces for a "disp(base)" memref, only stores the base and adds the disp in raw2trace post-processing, as it's statically known. The base can be directly written as it's already in a register, reducing scratch register pressure.
Moves the second scratch register reservation into the instru_t routines so we can skip it for this optimization of just writing the base reg for "disp(base)" memrefs.
Issue: #2001