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/jffs2/Kconfig b/fs/jffs2/Kconfig
index e69de29..1b9ecdd 100644
--- a/fs/jffs2/Kconfig
+++ b/fs/jffs2/Kconfig
@@ -0,0 +1,7 @@
+config FS_JFFS2
+	bool "Enable JFFS2 filesystem support"
+	help
+	  This provides support for reading images from JFFS2 (Journalling
+	  Flash File System version 2). JFFS2 is a log-structured file system
+	  for use with flash memory devices. It supports raw NAND devices,
+	  hard links and compression.