I think, you could attempt to compile an image from the checkout of the Github you found above. It seems to be (based on) work discussed in this thread: Working Realtek SoC RTL8196E 97D 97F in last master
This also seems relevant: Any plans for Realtek SOC support?
There are also other search hits on the forum for RTL8197D. Have you already attached a serial console?
Then you could attempt to cherry-pick relevant commits from that Repo, and attempt to apply them to a current openwrt master, or one of the 22.x, or 21.x releases.