google/chromeos: guard cbmem_find() in verstage and bootblock

When vboot_handoff_flag() is called in the bootblock or a separate
verstage there's no memory nor the possibility of dram coming online.
Therefore, don't bother to attempt call cbmem_find().

BUG=chrome-os-partner:44827
BRANCH=glados
TEST=Built chell with separate verstage which pulls in vboot_common.c
     dependency. No more linking errors w/ cbmem_find() not being
     around.

Change-Id: I494c93adc1c00459fdfaa8ce535c6b4c884ed0fb
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 414ce6aeaff657dc90289b25e5c883562189b154
Original-Change-Id: I8a5f2d154026ce794a70e7ec38883fa3c28fb6e7
Original-Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/324070
Original-Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://review.coreboot.org/13580
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/vendorcode/google/chromeos/vboot_common.c

@@ -20,6 +20,7 @@
 #include <console/console.h>
 #include <fmap.h>
 #include <reset.h>
+#include <rules.h>
 #include <stddef.h>
 #include <string.h>
 
@@ -41,6 +42,12 @@ int vboot_get_handoff_info(void **addr, uint32_t *size)
 {
 	struct vboot_handoff *vboot_handoff;
 
+	/* No flags are available in a separate verstage or bootblock because
+	 * cbmem only comes online when dram does. */
+	if ((ENV_VERSTAGE && IS_ENABLED(CONFIG_VBOOT_STARTS_IN_BOOTBLOCK)) ||
+		ENV_BOOTBLOCK)
+		return -1;
+
 	vboot_handoff = cbmem_find(CBMEM_ID_VBOOT_HANDOFF);
 
 	if (vboot_handoff == NULL)