Oh, too quick in replying :). You're changing the "cell" type which is used all over the place with sizeof() to figure out the cell size of guest visible (device tree) fields. I don't see how it could not be guest exposed.
Fix those bugs then. Those fields in the device tree are four bytes per integer, #address-cells etc. integers per item. The device tree does not expose the cell size of the underlying system anywhere.
Segher