intel/sandybridge: Add PCI ID for northbridge 0x150

Change-Id: I335244b7c39d6ddff6ecb06cb823fee09e35ee26
Signed-off-by: Damien Zammit <damien@zamaudio.com>
Reviewed-on: http://review.coreboot.org/7233
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>