soc/intel/broadwell: Rename `ramstage.h`

This file only contains the `broadwell_run_reference_code()` function
prototype (either a declaration or an inline stub definition). Rename
this file to refcode.h and only include it where necessary.

Tested with BUILD_TIMELESS=1, Purism Librem 13 v1 remains identical.

Change-Id: I6513f45b8914a84312b27ef4860870a89fd0aab3
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55582
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/soc/intel/broadwell/northbridge.c b/src/soc/intel/broadwell/northbridge.c
index 623ab70..76ea35f 100644
--- a/src/soc/intel/broadwell/northbridge.c
+++ b/src/soc/intel/broadwell/northbridge.c
@@ -12,7 +12,7 @@
 #include <soc/acpi.h>
 #include <soc/iomap.h>
 #include <soc/pci_devs.h>
-#include <soc/ramstage.h>
+#include <soc/refcode.h>
 #include <soc/systemagent.h>
 
 u8 systemagent_revision(void)