ramips: improve BDCOM WAP2100-SK support

Use the generic board detection instead of the target specific one as
all recent additions are doing.

Setup the USB led via devicetree (a5853577) and include the required
driver by default. Merge the led userspace setting with an existing
identical case.

Use the wps led for boot status indication.

Move the partitions into a partition table node (6031ab34) and drop
needless labels. Drop misplaced cells properties (53624c17).

Cleanup the pinmux and only switch pins to gpio functions which a
referenced as gpio in the dts.

Match the maximum image size with the size of the firmware partition.

Signed-off-by: Mathias Kresin <dev@kresin.me>