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/M52277EVB_stmicro_defconfig b/configs/M52277EVB_stmicro_defconfig
index 4f9d97e..d657f86 100644
--- a/configs/M52277EVB_stmicro_defconfig
+++ b/configs/M52277EVB_stmicro_defconfig
@@ -12,6 +12,7 @@
 # CONFIG_CMD_NFS is not set
 CONFIG_CMD_CACHE=y
 CONFIG_CMD_DATE=y
+CONFIG_CMD_JFFS2=y
 CONFIG_MTD_NOR_FLASH=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_STMICRO=y