Convert CONFIG_CMD_JFFS2 to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_JFFS2

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/ds414_defconfig b/configs/ds414_defconfig
index b637483..4e17bb9 100644
--- a/configs/ds414_defconfig
+++ b/configs/ds414_defconfig
@@ -26,6 +26,7 @@
 CONFIG_CMD_TIME=y
 CONFIG_CMD_EXT2=y
 CONFIG_CMD_FAT=y
+CONFIG_CMD_JFFS2=y
 CONFIG_CMD_UBI=y
 CONFIG_ISO_PARTITION=y
 CONFIG_SPL_OF_TRANSLATE=y