zeusminer: support added for ZeusMiner scrypt ASICs

--set zus:freq=XYZ (default 328)
--set zus:chips=X (default 6)
--set zus:cores=X (default 8)
--set zus:ignore_golden_nonce (don't check probe response - buggy HW/FW)
```
diff = work->nonce_diff * 0x10000;
```
Note that min_nonce_diff is set such that this can never be <1