src/northbridge: Add guards on all header files

Change-Id: I93b939478615f22f2c078b1efb7999ad4f3a4c28
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20747
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>
4 files changed