Allow dramsim_ini folder to be set at the command line

[colinschmidt]

verilator supports the amount of vpi we need to do our own argument parsing without messing with emulator.cc every time.

[davidbiancolin]

Nice cleanup. LGTM

[jwright6323]

Nice. Is there even a difference between this and rocket-chip's emulator.cc now?

[colinschmidt]

Rocket-chip doesn't support permissive (so doesn't support arbitrarty additions or verilator runtime arguments), it also doesn't support TSI.
We could probably crib the way they do async reset rising pulse, and then it would be a smaller diff but ours still adds several useful features for chipyard.