Asus RT-AX89X has an Qualcomm QCA8337 switch used to provide additional
1G copper ports, so lets enable qca8k in order to utilize DSA instead of
relying on SSDK for it.
Link: https://github.com/openwrt/openwrt/pull/15840
Signed-off-by: Robert Marko <robimarko@gmail.com>