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/suvd3_defconfig b/configs/suvd3_defconfig
index 68cfe65..e5e100a 100644
--- a/configs/suvd3_defconfig
+++ b/configs/suvd3_defconfig
@@ -17,6 +17,7 @@
 CONFIG_CMD_DHCP=y
 CONFIG_CMD_MII=y
 CONFIG_CMD_PING=y
+CONFIG_CMD_JFFS2=y
 CONFIG_CMD_UBI=y
 # CONFIG_MMC is not set
 CONFIG_MTD_NOR_FLASH=y