arm: sun8i: sunxi-h3-h5: Add dt node for the syscon control module

This patch add the dt node for the syscon register present on the
Allwinner H3/H5

Only two register are present in this syscon and the only one useful is
the one dedicated to EMAC clock..

Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>