arm64: dts: rockchip: enable gmac node on quartz64-a

Enable the gmac controller on the Pine64 Quartz64 Model A.

Signed-off-by: Peter Geis <pgwipeout@gmail.com>
Link: https://lore.kernel.org/r/20210728180034.717953-8-pgwipeout@gmail.com


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