mpc85xx: use bootwrapper for ws-ap3825i

mpc85xx: use bootwrapper for ws-ap3825i

The boot-procedure for the Extreme WS-AP3825I is vfragile to put it
mildly. It does not relocate the FDT properly. It currently exercises
every step manually as well as coming with a pre-padded dtb.

Use the PowerPC bootwrapper code for legacy platforms with a pre-filles
DTS instead. We still need to ship a fit image to not break the fdt
resize / relocate instructions on existing boards. This does not require
adapting the U-Boot bootcommand.

Ref: https://github.com/openwrt/openwrt/issues/12223

Signed-off-by: David Bauer <mail@david-bauer.net>