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/TQM823M_defconfig b/configs/TQM823M_defconfig
index b7c6462..0490828 100644
--- a/configs/TQM823M_defconfig
+++ b/configs/TQM823M_defconfig
@@ -11,6 +11,7 @@
 CONFIG_CMD_SNTP=y
 CONFIG_CMD_DATE=y
 CONFIG_CMD_EXT2=y
+CONFIG_CMD_JFFS2=y
 CONFIG_MAC_PARTITION=y
 CONFIG_DOS_PARTITION=y
 CONFIG_LED_STATUS=y