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)
I've gone through the Icarus code and determined:

* work_division is used to set nonce_mask
* it is also used to set fpga_count if fpga_count is not set
* fpga_count and nonce_mask are only used to calculate hashes when a nonce is found

Based on all of my testing (and other users / forks), it's not possible to get the nonce_mask / work_division combo to work with e.g. 60 chips and 8 cores each. The nonce_mask code is meant to take a power of 2 only.