soc/intel/common: Add mrc.cache file to CBFS when appropriate

The code in mrc_cache.c doesn't check for the presence of 'mrc.cache',
and just returns hardcoded value for he location of he MRC cache. This
becomes a problem when there is a CBFS file at the same location,
which can get overwritten. A CBFS file is created to cover this region
so that nothing can be added there.
This has the advantage of creating a build time error if another cbfs
file is hardcoded over the same region.

The default location of the MRC cache is also moved to 4G - 128K to
ensure that it defaults to something within CBFS.

Change-Id: Ic029c182f5a2180cb680e09b25165ee303a448a3
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-on: http://review.coreboot.org/11440
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/common/Kconfig

@@ -18,7 +18,7 @@ if CACHE_MRC_SETTINGS
 config MRC_SETTINGS_CACHE_BASE
 	hex
 	depends on !USE_FMAP
-	default 0xffb00000
+	default 0xfffe0000
 
 config MRC_SETTINGS_CACHE_SIZE
 	hex

src/soc/intel/common/Makefile.inc

@@ -17,4 +17,17 @@ ramstage-$(CONFIG_SOC_INTEL_COMMON_STAGE_CACHE) += stage_cache.c
 ramstage-$(CONFIG_PLATFORM_USES_FSP1_1) += util.c
 ramstage-$(CONFIG_GOP_SUPPORT) += vbt.c
 
+# Create and add the MRC cache to the cbfs image
+ifneq ($(CONFIG_CHROMEOS),y)
+$(obj)/mrc.cache: $(obj)/config.h
+	dd if=/dev/zero count=1 \
+	bs=$(shell printf "%d" $(CONFIG_MRC_SETTINGS_CACHE_SIZE) ) | \
+	tr '\000' '\377' > $@
+
+cbfs-files-$(CONFIG_CACHE_MRC_SETTINGS) += mrc.cache
+mrc.cache-file := $(obj)/mrc.cache
+mrc.cache-position := $(CONFIG_MRC_SETTINGS_CACHE_BASE)
+mrc.cache-type := mrc_cache
+endif
+
 endif