Tidy up imports in sim.py
Tidy up imports in sim.py

We now put sys.path back after importing things and no longer import
'*' from anything (which means static analysis tools can now spot when
we've got a name wrong).

lowRISC/ibex,AmbiML/ibex,lowRISC/ibex,lowRISC/ibex,AmbiML/ibex,AmbiML/ibex,AmbiML/ibex,lowRISC/ibex