ARM: dts: rockchip: Add gmac node for RK3128

RK3128's gmac is based on Synopsys Ethernet GMAC IP core.
Add it to the devicetree.

Signed-off-by: Alex Bee <knaerzche@gmail.com>
Link: https://lore.kernel.org/r/20231202124158.65615-3-knaerzche@gmail.com


Signed-off-by: Heiko Stuebner <heiko@sntech.de>