Many minor hotfix issued from the mixed precision branch

• Fix integration issues in C++ code (Discovered with Exageostat)
• Fix complex SPD matrix generation with latms
• Add RUNTIME_handle_to_tile() function to convert a runtime pointer to the associated CHAM_tile structure when needed outside chameleon
• Add CHAMELEON_GetContext() function to get the context in order to create its own algorithms outside chameleon.
• Fix registration of tiles with the mixed type
• Fix error message in fixdbl parameter function