- Rename keyword "gpu" -> "nvidia-gpu"
- Add keyword "amd-gpu"

Master pre stage

See merge request !58

Add missing variable to openmp clause shared

See merge request !57

Gpu in openmp code path

See merge request !56

The GPU logic has been implemented in the OpenMP code paths in ELPA2.
Currently, this implies that _internal_ to ELPA2, the number of OpenMP
threads is set to one (independent of how many threads the calling
application uses) and the original value is restored at the end of ELPA.
Though this is not the general case, this is _not_ a limitation, since
in the GPU case no work is done on the CPU and thus no threading is
helpful

For ELPA 1stage now you can use GPUs in the OpenMP enabled version
of ELPA. Currently this implies that within ELPA1 only _ONE_
OpenMP thread is used, independent of how many threads the calling
application uses

Assign tasks to gpu

See merge request !55