ARM: dts: rockchip: Add devicetree source for MarsBoard RK3066

This patch adds initial support for the Marsboard RK3066. It enables
EMAC Rockchip which is the ethernet support on the board and registers
it as a supported rockchip platform.

Signed-off-by: Romain Perier <romain.perier@gmail.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>