pwsafe gpu clean up and optimzation

Cleaned up a lot of the GPU pwsafe code and applied more optimizations.

Here are the benchmarks.
Device 1: Tahiti (AMD Radeon HD 7900 Series)
Local worksize (LWS) 64, Global worksize (GWS) 57344
Benchmarking: Password Safe SHA-256 [OpenCL]... DONE
Raw:	472615 c/s real, 17203K c/s virtual

Benchmarking: Password Safe SHA-256 [CUDA]... DONE
Raw:	129590 c/s real, 128862 c/s virtual