mpc85xx: Fix booting on various boards

commit 0e870980 ("8xxx: Removed
CONFIG_NUM_CPUS from 85xx/86xx") breaks U-Boot on various boards,
namely the ones that call get_sys_info() from board_early_init_f().

get_sys_info() calls cpu_numcores(), which depends on probecpu()
being called before. But probecpu() is called after board_early_init_f(),
and so cpu_numcores() returns random values, which in turn crashes
get_sys_info().

To fix the issue we place probecpu() before board_early_init_f()
in an initialization sequence.

Booting on the following boards should be revived now:
 mpc8540ads
 mpc8541cds
 mpc8548cds
 mpc8555cds
 mpc8560ads
 mpc8568mds
 mpc8569mds
 and maybe more.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>