soc/intel: Use common romstage code

This provides stack guards with checking and common
entry into postcar.

The code in cpu/intel/car/romstage.c is candidate
for becoming architectural so function prototype
is moved to <arch/romstage.h>.

Change-Id: I4c5a9789e7cf3f7f49a4a33e21dac894320a9639
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34893
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/northbridge/intel/gm45/romstage.c b/src/northbridge/intel/gm45/romstage.c
index 7c16761..c853a3a 100644
--- a/src/northbridge/intel/gm45/romstage.c
+++ b/src/northbridge/intel/gm45/romstage.c
@@ -21,7 +21,7 @@
 #include <device/pci_ops.h>
 #include <arch/acpi.h>
 #include <cpu/x86/lapic.h>
-#include <cpu/intel/romstage.h>
+#include <arch/romstage.h>
 #include <northbridge/intel/gm45/gm45.h>
 #include <southbridge/intel/i82801ix/i82801ix.h>
 #include <southbridge/intel/common/gpio.h>