OpenWRT tries to stay close to the mainline Linux kernel. I don't know much about these SoCs, but there is an archived post on the old OpenWRT forum here:
http://forum.archive.openwrt.org/viewtopic.php?id=46606
edit: newer thread: Working Realtek SoC RTL8196E 97D 97F in last master
Realtek took a (now very very old) version of Linux, and modified it to run on the 8196, but did not contribute their changes back to Linux. Because no volunteers merged their work (maybe the changes were too messy or large) at the time, it will be very large amount of work to add mainline Linux support at this stage. Possibly compiler patches would also be needed. I'd recommend picking a cheap SoC with mainline Linux support already (another Realtek if you like, or maybe an Allwinner or Rockchip etc.).