powerpc/8xxx: Introduce 85xx, 86xx, QorIQ config headers

Add new headers that capture common defines for a given SoC/processor
rather than duplicating that information in board config.h and random
other places.

Eventually this should be handled by Kconfig & defconfigs

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Acked-by: Wolfgang Denk <wd@denx.de>