mb/amd/birman: Improve missing APCB warning

Move the missing APCB warning to the end of the build and make it stand
out better. Prior to this patch, the warning would appear as one of the
first build messages and easily be missed due to the rest of the build
messages.

TEST=build with and without proper APCBs being found, warning message
appears only when APCB is not found and stands out more

Signed-off-by: Fred Reitberger <reitbergerfred@gmail.com>
Change-Id: Iabe32636b8e31fe781519533a329a08535bd661a
Reviewed-on: https://review.coreboot.org/c/coreboot/+/72901
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
diff --git a/src/mainboard/amd/birman/Makefile.inc b/src/mainboard/amd/birman/Makefile.inc
index e214337..c60bf9c 100644
--- a/src/mainboard/amd/birman/Makefile.inc
+++ b/src/mainboard/amd/birman/Makefile.inc
@@ -14,9 +14,15 @@
 APCB_SOURCES = $(MAINBOARD_BLOBS_DIR)/APCB_Updatable.bin
 APCB_SOURCES_RECOVERY = $(MAINBOARD_BLOBS_DIR)/APCB_DefaultRecovery.bin
 else
-$(info APCB sources not found. Skipping APCB. The resulting image won't boot.)
+files_added:: warn_no_apcb
 endif
 
+PHONY+=warn_no_apcb
+warn_no_apcb:
+	printf "\n\t** WARNING **\n"
+	printf "coreboot has been built without an APCB.\n"
+	printf "This image will not boot.\n\n"
+
 ifeq ($(CONFIG_BIRMAN_HAVE_MCHP_FW),y)
 $(call add_intermediate, add_mchp_fw)
 	$(CBFSTOOL) $(obj)/coreboot.pre write -r EC -f $(CONFIG_BIRMAN_MCHP_SIG_FILE) --fill-upward