bmips: use wan ports as standalone ports

bmips: use wan ports as standalone ports

With the recent fixes backported to 6.12, b53 ports should now fully
work as standalone ports outside of a switch.

So move them out of the switch and use them as standalone ports, which
makes configuring easier as VLANs don't need to be defined and reserved
anymore to use the wan port.

Tested on DGND3700v1.

While most devices do not define a wan port, I dropped the
ucidef_set_bridge_device() from all devices for consistency.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>