[POWERPC] 8xx: Get rid of conditional includes of board specific setup

Directly include mpc885ads.h from mpc885ads_setup.c. Now we can get rid
of the arch dependent includes in mpc8xx.h.

Signed-off-by: Jochen Friedrich <jochen@scram.de>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>