arm: dts: revpi-flat-s-2022: Use dwc2 usb (this blocks [REVPI-3831])

The XHCI usb controller can only be used if otg_mode=1 is present in /boot/config.txt. Although Raspberry Pi is about to relase an updated version of their bootloader which can detect if the xhci controller is wanted from dt, we cannot use this feature without a proper release from them. Thus use the dwc2 controller like we do on other devices for now.

Signed-off-by: Nicolai Buchwitz n.buchwitz@kunbus.com