PME GPU/CUDA data framework.

PME GPU/CUDA data framework.

This patch adds most of the PME GPU data handling routines
(pme.h and pme-gpu.cpp / pme.cu(h) / pme-gpu-internal.h/cpp),
data structures used on host and on device
(pme-gpu-types.h / pme.cuh).
The PME GPU kernels and their host code will live in separate files.
There is also cuFFT code (pme-3dfft.cu(h)) and
optional CUDA timing events (pme-timings.cu(h)) included.
Currently this is a dead code, PME GPU is not actually getting initialized
as the corresponding enum is always set for CPU path, which is asserted.

Change-Id: I9b03f54a2412885e25ea27f17bf2dca1b01f9f78