Mismatch between bus address width and addresses passed through vhdmmio

Bus address width is a generic on the top-levels, but it's not a generic for the widths of output registers for vhdmmio (understandibly).

The easiest way to fix this would be to remove the generic from the top-level and only allow it to be set through the command-line parameters of Fletchgen.

Another way to fix it would be to resize it before it enters the corresponding ACCM instance at the nucleus level, but it would be a bit obscure, since the generated vhdmmio docs won't convey the limited number of bits used to represent addresses.