m68k/defconfig: Make NFS_V4 modular instead of builtin

This reduces the kernel image size by ca. 100 KiB, while still allowing
NFS root.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
diff --git a/arch/m68k/configs/atari_defconfig b/arch/m68k/configs/atari_defconfig
index 6d5370c..fa33639 100644
--- a/arch/m68k/configs/atari_defconfig
+++ b/arch/m68k/configs/atari_defconfig
@@ -360,7 +360,7 @@
 CONFIG_SYSV_FS=m
 CONFIG_UFS_FS=m
 CONFIG_NFS_FS=y
-CONFIG_NFS_V4=y
+CONFIG_NFS_V4=m
 CONFIG_NFS_SWAP=y
 CONFIG_ROOT_NFS=y
 CONFIG_NFSD=m