sandy/ivy: Fix mrc.cache file in CBFS

The file was not recreated when configuration changed. One would
hit this bug when turning CHROMEOS on/off.

Also do not create mrc.cache with CHROMEOS at all.

Change-Id: I5b0ecde66589396b24967ce289bf65e20bb08825
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/5211
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@google.com>

src/northbridge/intel/sandybridge/Makefile.inc

@@ -40,7 +40,8 @@ mrc.bin-file := $(call strip_quotes,$(CONFIG_MRC_FILE))
 mrc.bin-position := 0xfffa0000
 mrc.bin-type := 0xab
 
-$(obj)/mrc.cache:
+ifneq ($(CONFIG_CHROMEOS),y)
+$(obj)/mrc.cache: $(obj)/config.h
 	dd if=/dev/zero count=1 \
 	bs=$(shell printf "%d" $(CONFIG_MRC_CACHE_SIZE) ) | \
 	tr '\000' '\377' > $@
@@ -49,5 +50,6 @@ cbfs-files-$(CONFIG_HAVE_MRC_CACHE) += mrc.cache
 mrc.cache-file := $(obj)/mrc.cache
 mrc.cache-position := 0xfffd0000
 mrc.cache-type := 0xac
+endif
 
 $(obj)/northbridge/intel/sandybridge/acpi.ramstage.o : $(obj)/build.h