Modifiy Makefile so that we can get board ID in verstage. BRANCH=none BUG=b:117916698 TEST=manually Change-Id: Idcdb6e07f565c937185cab811abac0ce47e5e3a7 Signed-off-by: You-Cheng Syu <youcheng@google.com> Reviewed-on: https://review.coreboot.org/c/31006 Tested-by: build bot (Jenkins) <no-reply@coreboot.org> Reviewed-by: Hung-Te Lin <hungte@chromium.org>