what-jenkins-does: make its payload selection overridable

Change-Id: Ifbdc6bf73595a0d04a8ae09c80394787b6f76d13
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: http://review.coreboot.org/11096
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
diff --git a/Makefile.inc b/Makefile.inc
index 2a4eaf6..0cb597f 100644
--- a/Makefile.inc
+++ b/Makefile.inc
@@ -680,7 +680,7 @@
 $(obj)/board_id:
 	printf $(CONFIG_BOARD_ID_STRING) > $@
 
-JENKINS_PAYLOAD=none
+JENKINS_PAYLOAD?=none
 what-jenkins-does:
 	util/abuild/abuild -B -J $(if $(JENKINS_NOCCACHE),,-y) -c 4 -z -p $(JENKINS_PAYLOAD)
 	(cd payloads/libpayload; unset COREBOOT_BUILD_DIR; $(MAKE) $(if $(JENKINS_NOCCACHE),,CONFIG_LP_CCACHE=y) V=$(V) Q=$(Q) junit.xml)