nb/intel/i440bx: Compile debug.c only if CONFIG_DEBUG_RAM_SETUP

... is enabled. Otherwise we are compiling an effectively
empty file.

Change-Id: I4e3d982066d1fa66a3da5f37e278ec7fd5bb1ea8
Signed-off-by: Keith Hui <buurin@gmail.com>
Reviewed-on: https://review.coreboot.org/21023
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Idwer Vollering <vidwer@gmail.com>

src/northbridge/intel/i440bx/Makefile.inc

@@ -19,6 +19,6 @@ ifeq ($(CONFIG_NORTHBRIDGE_INTEL_I440BX),y)
 ramstage-y += northbridge.c
 
 romstage-y += raminit.c
-romstage-y += debug.c
+romstage-$(CONFIG_DEBUG_RAM_SETUP) += debug.c
 
 endif