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>

src/soc/intel/broadwell/pch/lpc.c

@@ -16,7 +16,6 @@
 #include <soc/pch.h>
 #include <soc/pci_devs.h>
 #include <soc/pm.h>
-#include <soc/ramstage.h>
 #include <soc/rcba.h>
 #include <soc/intel/broadwell/pch/chip.h>
 #include <acpi/acpigen.h>