Use cudaLaunchKernel with CUDA 7.0 and later

Use cudaLaunchKernel with CUDA 7.0 and later

CUDA 7.0 introduced the cudaLaunchKernel API call similar to the
CUDA driver API and avoids the chevron notation. This has the benefit
of a slight reduction in runtime API overhead (up to 2%) partly
because two runtime API calls that precede the kernel launch are skipped
(cudaSetupArgument and cudaConfigureCall).

For future dev-testing the GMX_DISABLE_CUDALAUNCH env. var. can be used to
force the chevron-notation kernel launch.

Change-Id: Id057fb01489814b99ae290de9e4ddd9f530a04be