cpu/intel/model_206ax: Switch to POSTCAR_STAGE

Tested on Lenovo Thinkpad X220 with both native raminit and mrc.bin.

Change-Id: I5e1a1175d79af4dc079a5a08a464eef08de0bcbf
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/26791
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
diff --git a/src/northbridge/intel/sandybridge/Makefile.inc b/src/northbridge/intel/sandybridge/Makefile.inc
index d08b141..3d8da0c 100644
--- a/src/northbridge/intel/sandybridge/Makefile.inc
+++ b/src/northbridge/intel/sandybridge/Makefile.inc
@@ -46,4 +46,6 @@
 
 smm-$(CONFIG_HAVE_SMI_HANDLER) += finalize.c
 
+postcar-y += ram_calc.c
+
 endif