Add cuFFT to Makefile.lassen_kokkos and generalize MPI path

# lassen_kokkos = KOKKOS/CUDA, V100 GPU and Power9, IBM Spectrum MPI, nvcc compiler with gcc 7.3.1

# lassen_kokkos = KOKKOS/CUDA, V100 GPU and Power9, IBM Spectrum MPI, nvcc compiler with gcc

SHELL = /bin/sh

# PATH = path for MPI library

# LIB = name of MPI library

MPI_INC = -DMPICH_SKIP_MPICXX -DOMPI_SKIP_MPICXX=1 -I/usr/tce/packages/spectrum-mpi/spectrum-mpi-rolling-release-gcc-7.3.1/include

MY_MPI_EXE = $(shell which mpicxx)

MY_MPI_PATH = $(dir ${MY_MPI_EXE})

MPI_INC =       -DMPICH_SKIP_MPICXX -DOMPI_SKIP_MPICXX=1 -I${MY_MPI_PATH}../include

MPI_PATH = 

MPI_LIB = -L/usr/tce/packages/spectrum-mpi/spectrum-mpi-rolling-release-gcc-7.3.1/lib -lmpi_ibm

MPI_LIB = -L${MY_MPI_PATH}../lib -lmpi_ibm

# FFT library

# see discussion in Section 2.2 (step 6) of manaul

# PATH = path for FFT library

# LIB = name of FFT library

FFT_INC =    	

FFT_INC = -DFFT_CUFFT

FFT_PATH = 

FFT_LIB =	

FFT_LIB = -lcufft

# JPEG and/or PNG library

# see discussion in Section 2.2 (step 7) of manual