unify cpu cryptonight implementations

xmr-stak has several implementations for multi hash per thread.
The results into 3 intepedent implementations.
Each time the algorithm must be changed the possibility to introduce errors is very large.

- unify the different cryptonight CPU implementations
- simplify the function selection array to find the specilized cryptonight implementation
- add a intermediat pointer to access the large state (similar to the old multi hash implementation)

As side effect this change increases the speed of the single and multi hash algorithm.

xmrstak/backend/amd/minethd.cpp

@@ -252,7 +252,7 @@ void minethd::work_main()
 
 				*(uint32_t*)(bWorkBlob + 39) = results[i];
 
-				hash_fun(bWorkBlob, oWork.iWorkSize, bResult, cpu_ctx);
+				hash_fun(bWorkBlob, oWork.iWorkSize, bResult, &cpu_ctx);
 				if ( (*((uint64_t*)(bResult + 24))) < oWork.iTarget)
 					executor::inst()->push_event(ex_event(job_result(oWork.sJobID, results[i], bResult, iThreadNo, miner_algo), oWork.iPoolId));
 				else

xmrstak/backend/amd/minethd.hpp

@@ -24,7 +24,7 @@ class minethd  : public iBackend
 	static bool init_gpus();
 
 private:
-	typedef void (*cn_hash_fun)(const void*, size_t, void*, cryptonight_ctx*);
+	typedef void (*cn_hash_fun)(const void*, size_t, void*, cryptonight_ctx**);
 
 	minethd(miner_work& pWork, size_t iNo, GpuContext* ctx, const jconf::thd_cfg cfg);