Add support for D-Link COVR-X1860

The branch: https://github.com/RolandoMagico/openwrt/tree/COVR-X1860-Mesh
The images: https://github.com/RolandoMagico/openwrt-build/releases/tag/COVR-X1860_Build_20230806_Mesh

I hope I didn't miss anything. I just did a short test with the sysupgrade image