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/ms7722se_defconfig b/configs/ms7722se_defconfig
index cb50b46..92f3158 100644
--- a/configs/ms7722se_defconfig
+++ b/configs/ms7722se_defconfig
@@ -20,5 +20,6 @@
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_PING=y
 # CONFIG_CMD_MISC is not set
+CONFIG_CMD_JFFS2=y
 CONFIG_MTD_NOR_FLASH=y
 CONFIG_USE_PRIVATE_LIBGCC=y