[S390] defconfig: switch on CONFIG_DEVTMPFS

Switching on the DEVTMPFS kernel option helpes to maintain a /dev
file system early in the boot process, especially, in limited
environments.
Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/defconfig

@@ -68,7 +68,7 @@ CONFIG_NET_CLS_RSVP6=m
 CONFIG_NET_CLS_ACT=y
 CONFIG_NET_ACT_POLICE=y
 CONFIG_UEVENT_HELPER_PATH="/sbin/hotplug"
-# CONFIG_FIRMWARE_IN_KERNEL is not set
+CONFIG_DEVTMPFS=y
 CONFIG_BLK_DEV_LOOP=m
 CONFIG_BLK_DEV_NBD=m
 CONFIG_BLK_DEV_RAM=y