move enum{NSQ,BIN,MULTI} to the Neighbor class in neighbor.h

src/KOKKOS/nbin_kokkos.cpp

src/KOKKOS/neigh_list_kokkos.cpp

src/KOKKOS/neighbor_kokkos.cpp

src/USER-INTEL/fix_intel.cpp

src/nbin_standard.cpp

src/neigh_list.cpp

src/neighbor.cpp

src/neighbor.h

src/nstencil.cpp