vtkm cont fails to compile with cuda 7.5

vtk-m/vtkm/cont/cuda/internal/CudaAllocator.cu(206): error: class "cudaDeviceProp" has no member "concurrentManagedAccess"

gcc 4.9.2 cuda 7.5

Also verified (and originally reported by @jameskress ) that the same compile error is generated on Titan.