intel post-car: Separate files for setup_stack_and_mtrrs()

Have a common romstage.c file to prepare CAR stack guards.

MTRR setup around cbmem_top() is somewhat northbridge specific,
place stubs under northbridge for platrform that will move
to RELOCATABLE_RAMSTAGE.

Change-Id: I3d4fe4145894e83e5980dc2a7bbb8a91acecb3c6
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/15762
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
diff --git a/src/northbridge/intel/x4x/ram_calc.c b/src/northbridge/intel/x4x/ram_calc.c
index 5a6a767..09eec47 100644
--- a/src/northbridge/intel/x4x/ram_calc.c
+++ b/src/northbridge/intel/x4x/ram_calc.c
@@ -23,6 +23,7 @@
 #include <arch/io.h>
 #include <device/pci_def.h>
 #include <console/console.h>
+#include <cpu/intel/romstage.h>
 #include <northbridge/intel/x4x/x4x.h>
 
 /** Decodes used Graphics Mode Select (GMS) to kilobytes. */
@@ -93,3 +94,8 @@
 	u32 ramtop = pci_read_config32(PCI_DEV(0,0,0), D0F0_TSEG);
 	return (void*)(ramtop);
 }
+
+void *setup_stack_and_mtrrs(void)
+{
+	return (void*)CONFIG_RAMTOP;
+}