This SoC is based on the TrendChip platform later acquired by Ralink, which was then acquired by Mediatek. There is a tool called tcrevenge to unpack firmware files, not sure if this is applicable for this device as well. But the tclinux toolchain is probably no longer maintained, and due to the lack of documentation there probably will never be official OpenWrt support, yet Mediatek/EcoNet still sell these chips for VDSL routers.