ARM: sun8i: a83t: Add dt node for the syscon control module

This patch add the dt node for the syscon register present on the
Allwinner A83T

Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>