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)
Can you advise on how to incorporate zeusminer_calc_target_diff() based on using work->nonce_diff instead? This was a fix that was required by jstefanop in the Darkwinde fork to get the ASIC to work with some difficulties.