sunxi: Enable UBI and NAND support

Enable the NAND and UBI support in the configuration header so that we can
(finally) use it.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Jagan Teki <jagan@openedev.com>