nb/intel/x4x: Define and use default MMCONF_BASE_ADDRESS

Currently only one board uses this northbridge in coreboot but some
patches are pending to add more.

Change-Id: If035e442d1a23674667f46a07b44c4f2b81be48c
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/19650
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
2 files changed