Remove individual cuda libraries

Instead use CUDA_ADD_LIBRARY to build libgromacs. It builds all
non CUDA files using the standard build rules. Thus this should not
have any effect on non CUDA files. All CUDA files were compiled
with the same nvcc OPTIONS, and thus nothing should have changed
for them either.

This also removes the requirement for gmxManageNvccConfig to set
fPIC manually because now CUDA_ADD_LIBRARY knows when the library
is shared.

Change-Id: I23fe6b7a9766a39c525cdc1abfa3922ec24058d9