This initialisation causes Xcelium to complain about multiple drivers
for the variable. Which is rather confusing, but we don't actually
need to initialise it: the variable will be X at the start of time, so
the logic that stops the simulation if it gets big won't fire until
after reset anyway.
Fix all remaining issues reported by Verible lint.
It turns out that #965 undid some of the fixes in `ibex_alu.sv`
that were done in #980 around the `SHUFFLE_*`/`FLIP_*` signals.
Simple system is a basic verilator top-level testbench for running
executables. It has functionality for outputting text to a log file
and for the software to terminate the simulation
