[POWERPC] 8xx: Fix wrapper platform for adder875, and combine defconfigs.

This fixes the following bug:
http://ozlabs.org/pipermail/linuxppc-dev/2008-February/051979.html

Separate defconfigs are no longer needed now that CONFIG_DEVICE_TREE is gone.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>