lib/timestamp: Add timestamps to CBMEM in POSTCAR stage

POSTCAR stage has cbmem online. So, all timestamps need to be added to
cbmem timestamp region.

BUG=chrome-os-partner:55848
TEST=Verified that timestamps added in postcar show up in cbmem -t.

Change-Id: I64af8c1e67b107d9adb09de57c20ea728981f07c
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/16032
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
diff --git a/src/lib/timestamp.c b/src/lib/timestamp.c
index 372076c..d8b93f9 100644
--- a/src/lib/timestamp.c
+++ b/src/lib/timestamp.c
@@ -49,7 +49,7 @@
 /* The cache location will sit in BSS when in ramstage. */
 #define TIMESTAMP_CACHE_IN_BSS ENV_RAMSTAGE
 
-#define HAS_CBMEM (ENV_ROMSTAGE || ENV_RAMSTAGE)
+#define HAS_CBMEM (ENV_ROMSTAGE || ENV_RAMSTAGE || ENV_POSTCAR)
 
 /* Storage of cache entries during ramstage prior to cbmem coming online. */
 static struct timestamp_cache timestamp_cache;