soc/intel/common/mrc_cache: Don't assume FMAP is tied to CHROMEOS

The old code only checked for an RW_MRC_CACHE region when
CONFIG_CHROMEOS was selected. This assumption is not necessarily true,
as one can have FMAP without a CHROMEOS build. As a result, always
search FMAP first before falling back on CBFS for locating the MRC
cache region.
The old logic where CHROMEOS builds would fail when RW_MRC_CACHE was
not found is preserved, such that behavior does not change.

Change-Id: I3596ef3235eff661af055968ea641f3e9671cdcd
Signed-off-by: Alexandru Gagniuc <alexandrux.gagniuc@intel.com>
Reviewed-on: https://review.coreboot.org/14757
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/common/mrc_cache.c

@@ -35,23 +35,27 @@ struct mrc_data_region {
 /* common code */
 static int mrc_cache_get_region(struct mrc_data_region *region)
 {
-	if (IS_ENABLED(CONFIG_CHROMEOS)) {
+	bool located_by_fmap = true;
 	struct region_device rdev;
 
 	if (fmap_locate_area_as_rdev("RW_MRC_CACHE", &rdev))
+		located_by_fmap =  false;
+
+	/* CHROMEOS builds must get their MRC cache from FMAP. */
+	if (IS_ENABLED(CONFIG_CHROMEOS) && !located_by_fmap)
 		return -1;
 
+	if (located_by_fmap) {
 		region->size = region_device_sz(&rdev);
 		region->base = rdev_mmap_full(&rdev);
 
 		if (region->base == NULL)
 			return -1;
-
-		return 0;
 	} else {
 		region->base = (void *)CONFIG_MRC_SETTINGS_CACHE_BASE;
 		region->size = CONFIG_MRC_SETTINGS_CACHE_SIZE;
 	}
+
 	return 0;
 }