Code divergence of real/complex CPU part in trans_ev_band_to_full

The real/complex CPU parts of trans_ev_band_to_full diverged:

The real code path uses blocking, the complex part does not!

To do:

• make blocking in real part an OPTION, i.e. a fall back to same code path as the complex version should be possible
• implement blocking for complex part also OPTIONAL.

In this way, we retain better tuning options for different architectures