nb/intel/pineview: Switch to POSTCAR_STAGE

Change-Id: If23925e2837645c974e4094e7e2d90e700d3d9e8
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/26786
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/northbridge/intel/pineview/Makefile.inc

@@ -25,4 +25,6 @@ romstage-y += ram_calc.c
 romstage-y += raminit.c
 romstage-y += early_init.c
 
+postcar-y += ram_calc.c
+
 endif