nfp: add Makefiles to all directories

To be able to build separate objects we need to provide
Kbuild with a Makefile in each directory.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/netronome/nfp/bpf/Makefile

+# SPDX-License-Identifier: GPL-2.0
+# kbuild requires Makefile in a directory to build individual objects

drivers/net/ethernet/netronome/nfp/flower/Makefile

+# SPDX-License-Identifier: GPL-2.0
+# kbuild requires Makefile in a directory to build individual objects

drivers/net/ethernet/netronome/nfp/nfpcore/Makefile

+# SPDX-License-Identifier: GPL-2.0
+# kbuild requires Makefile in a directory to build individual objects

drivers/net/ethernet/netronome/nfp/nfpcore/nfp6000/Makefile

+# SPDX-License-Identifier: GPL-2.0
+# kbuild requires Makefile in a directory to build individual objects

drivers/net/ethernet/netronome/nfp/nic/Makefile

+# SPDX-License-Identifier: GPL-2.0
+# kbuild requires Makefile in a directory to build individual objects