fs: Kconfig: Add a separate option for FS_JFFS2

Rather than using CMD_JFFS2 for both the filesystem and its command, we
should have a separate option for each. This allows us to enable JFFS2
support without the command, if desired, which reduces U-Boot's size
slightly.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/fs/Makefile b/fs/Makefile
index 5c90656..5770f41 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -16,7 +16,7 @@
 obj-$(CONFIG_CMD_CRAMFS) += cramfs/
 obj-$(CONFIG_FS_EXT4) += ext4/
 obj-y += fat/
-obj-$(CONFIG_CMD_JFFS2) += jffs2/
+obj-$(CONFIG_FS_JFFS2) += jffs2/
 obj-$(CONFIG_CMD_REISER) += reiserfs/
 obj-$(CONFIG_SANDBOX) += sandbox/
 obj-$(CONFIG_CMD_UBIFS) += ubifs/