mpc85xx: configs: remove c=ffe from default environment

AFAICT, c=ffe does nothing and was a typo from the original commit
d1712369 "powerpc/p4080: Add support
for the P4080DS board" and just kept on getting duplicated
in subsequently added board config files.

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Acked-by: Edward Swarthout <ed.swarthout@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>