Thank you very much, that did the trick!
I simply appended
&usb_phy0 {
status = "okay";
};
&usb0 {
#address-cells = <1>;
#size-cells = <0>;
status = "okay";
hub_port0: port@1 {
reg = <1>;
#trigger-source-cells = <0>;
};
};
to the file target/linux/ath79/dts/qca9563_tplink_archer-c6-v2.dts and then the USB root hub showed up in dmesg, as well as info about plugging and unplugging devices.