#2229 was not solving the issues

- revert #2229
- introduce the working fix

The OpenCl version of the blockchain driver is not understanding if
apointer to a pointer points into shared memory and throw an error
during the compilation.

- revert the usage of the struct to group all shared memory arrays

Add seperate kernel to prepare the scratchpad memory.

Combine the shared memory for a hash within one struct.
Reduce the shared memory footprint per hash by 64 byte.

- rename variable names like `b` and `bb` to something with a little bit
of meaning.

Optimize cn_gpu

- use the user defined unroll
- auto suggestion:
  - only tune for cn_gpu if this is the main user
currency (after a fork)
  - set unroll to 1 for cn_gpu

If comp_mode is used the code will not compile.

- fix compile issue
- fix wrong conditions to handle `comp_mode`

Co-authored-by: psychocrypt <psychocryptHPC@gmail.com>
Co-authored-by: fireice-uk <fireice-uk@users.noreply.github.com>