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/TQM855M_defconfig b/configs/TQM855M_defconfig
index bf1186a..faab826 100644
--- a/configs/TQM855M_defconfig
+++ b/configs/TQM855M_defconfig
@@ -12,6 +12,7 @@
 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