nb/intel/sandybridge: Move steppings to CPU header

The steppings correspond to the CPUID bits 3:0, so move them to the CPU
scope, and include the CPU header from files using the stepping macros.

Change-Id: Idf8fba4911f98953bb909777aea57295774d8400
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48409
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/northbridge/intel/sandybridge/raminit_native.c b/src/northbridge/intel/sandybridge/raminit_native.c
index 0d581f5..9961e89 100644
--- a/src/northbridge/intel/sandybridge/raminit_native.c
+++ b/src/northbridge/intel/sandybridge/raminit_native.c
@@ -3,6 +3,7 @@
 #include <commonlib/clamp.h>
 #include <console/console.h>
 #include <console/usb.h>
+#include <cpu/intel/model_206ax/model_206ax.h>
 #include <delay.h>
 #include <device/device.h>
 #include <device/pci_def.h>