K-computer specific modifications

This commit implements most of the K-computer-
specific changes for Gromacs-5.0. The HPC-ACE
SIMD module has been added since we need the
exponentials for LJPME, and there are also some
fixes to the LJPME nonbonded accelerated group
kernels that prevented them from compiling.
The SIMD unit tests have been modified to avoid
making assumptions about the internal storage
being single or double, since HPC-ACE only
supports double. The toolchain files have
been updated and moved to the platform subdir,
and we now have a separate module to handle
Gromacs-specific flags and settings for K.

Change-Id: I5b832809b5dd52ef4b72f6cd41b1b3da1c036a57