These are DTS configuration to allow the qca-nss-gmac driver to probe and attached itself to drive the GMAC ports. The standard OpenWRT repo comes with the stmmac driver, which had to be disable. The NSS core drivers depends on the qca-nss-gmac driver so the stmmac driver have to be prevented from successfully probing and take over the GMAC port.
My repo tries to enable support for both drivers with the DTS configuration, relying manually disabling the stmmac driver via kernel build configuration. Actually this is not necessary. Changing the DTS files to force the use of the qca-nss-gmac driver is correct.