haswell: relocate `romstage_common` to northbridge

Other platforms do this as well. It will ease refactoring on follow-ups.

Change-Id: I643982a58c6f5370c78acef93740f27df001a06d
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43093
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tristan Corrick <tristan@corrick.kiwi>
diff --git a/src/northbridge/intel/haswell/Makefile.inc b/src/northbridge/intel/haswell/Makefile.inc
index 8ef3079..b2fd530 100644
--- a/src/northbridge/intel/haswell/Makefile.inc
+++ b/src/northbridge/intel/haswell/Makefile.inc
@@ -14,6 +14,7 @@
 
 romstage-y += memmap.c
 romstage-y += raminit.c
+romstage-y += romstage.c
 romstage-y += early_init.c
 romstage-y += report_platform.c