Discussion about common code.

I can show you what i did and discuss the find_best_gws stuff.

I like the 'verbose' find_best_gws. The 'quiet' one was suboptimal, making both follow the same rules seems to be enough for all formats using shared code (now).

In order to understand the amount of code in this patch.
- muted opencl_find_best_lws as you did for GWS.
- I moved more code to common file (my files). 
- I need to revert 8746ef4 (it doesn't hurt - i prefer to revert it later).
- Maybe revert c8a0c08 (the maintainer has to decide to use the shared code).
- If c8a0c08 is not reverted, maybe move more common code from 'opencl_sha2_common.c' to 'common-opencl.c'.