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/cmd/Kconfig b/cmd/Kconfig
index e4cb6c9..be6b314 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1147,6 +1147,7 @@
 
 config CMD_JFFS2
 	bool "jffs2 command"
+	select FS_JFFS2
 	help
 	  Enables commands to support the JFFS2 (Journalling Flash File System
 	  version 2) filesystem. This enables fsload, ls and fsinfo which