dts: rk3399: add gmac for the rk3399

This change adds the gmac node (i.e. the GMAC Ethernet controller) as
defined in the Linux DTS.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Simon Glass <sjg@chromium.org>
1 file changed