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/TQM5200S_defconfig b/configs/TQM5200S_defconfig
index 4ed119d..d0c352f 100644
--- a/configs/TQM5200S_defconfig
+++ b/configs/TQM5200S_defconfig
@@ -17,6 +17,7 @@
 CONFIG_CMD_BSP=y
 CONFIG_CMD_EXT2=y
 CONFIG_CMD_FAT=y
+CONFIG_CMD_JFFS2=y
 CONFIG_CMD_DIAG=y
 CONFIG_MAC_PARTITION=y
 CONFIG_ISO_PARTITION=y