ARM: exynos_defconfig: Enable options to mount a rootfs via NFS

This patch enables the options to mount a rootfs over NFS and also
support for automatic configuration of IP addresses during boot as
needed by NFS.

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Kukjin Kim <kgene@kernel.org>