ARM: shmobile: koelsch: Enable DEVTMPFS_MOUNT in defconfig

Without this, a Debian jessie nfsroot hangs early in the boot process.

Signed-off-by: Geert Uytterhoeven <geert+renesas@linux-m68k.org>
[horms+renesas@verge.net.au: resolved trivial conflict]
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>