Waive Verilator Warnings

Created by: zarubaf

As discussed in last week's meeting, this waives all the Verilator warnings, so that we at least do not introduce new ones.

The only warning that I've waived in general is UNOPTFLAT which is Verilator trying to tell us that the resulting code can't be optimized.

I think we should at least fix:

• PINCONNECTEMPTY
• IMPLICIT
• UNDRIVE
• MULTIDRIVE
• and potentially UNUSED