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/cam5200_defconfig b/configs/cam5200_defconfig
index 46a24f5..d8a419c 100644
--- a/configs/cam5200_defconfig
+++ b/configs/cam5200_defconfig
@@ -13,6 +13,7 @@
 CONFIG_CMD_PING=y
 CONFIG_CMD_SNTP=y
 CONFIG_CMD_BSP=y
+CONFIG_CMD_JFFS2=y
 CONFIG_MAC_PARTITION=y
 CONFIG_DOS_PARTITION=y
 CONFIG_ISO_PARTITION=y