Difftest is not compatible with Chisel Definition/Instance

[poemonsense]

Chisel has experimental features of Definition/Instance to avoid multiple elaboration of the same hardware. However, this brings issues to the elaboration of Difftest, which relies on the generational information during Chisel elaboration. See OpenXiangShan/XiangShan#2338

Don't know how to fix it yet.

[poemonsense]

#714 makes this issue more severe because in most cases DiffTest will use bore to wiring the interfaces to the top.

XiangShan-nanhu is not compatible with the latest DiffTest (with its current IntWriteback mechanism).

XiangShan-KMH seems OK because it does not use Definition/Instance.