amd southbirdge sb800 wrapper, pci bridge fix

amd southbirdge sb800 wrapper, pci bridge fix

sb800 pci bridge SHOULD enabled by default according to the chipset document,
but actually not enabled on some mainboard.
enable sb800 pci bridge when told to enable in devicetree.cb.
tested on ibase persimmon mainboard.

Change-Id: I42075907b4a003b2e58e5b19635a2e1b3fe094c3
Signed-off-by: Kerry She <shekairui@gmail.com>
Reviewed-on: http://review.coreboot.org/63
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>