ARM: dts: sun8i: a83t: add dwmac-sun8i device node

The dwmac-sun8i is an ethernet MAC hardware that support 10/100/1000 speed.
This patch add support for it on the Allwinner a83t SoC Device-tree.

This patch add the emac device node and the related RGMII pins node.

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