mpc85xx: convert WS-AP3710i to simpleImage wrapper

mpc85xx: convert WS-AP3710i to simpleImage wrapper

Convert the Enterasys WS-AP3710i access point to use the simpleImage
wrapper.

This is necessary, as the bootlaoder does not align the DTB correctly
(and does not support altering the FDT loadaddress). Booting images with
kernels 5.15 and later can break depending on the alignment on the DTB
within the FIT image.

Compared with the patch applied to master, this compiles the loader at
the changed offset used in OpenWrt master. This is required, as U-Boot
loads the uImage at the offset the loader is currently compiled for.

Signed-off-by: David Bauer <mail@david-bauer.net>
(cherry picked from commit eec18118d02fa5d095cb4035c42187e487d0e68c)