project-lakitu: fix official signing process for ARM64

Satsify assumption made in sign_official_build.sh by creating
a dummy .cfg file in /syslinux/ dir on ESP.

BUG=b/176990752
TEST=presubmit
RELEASE_NOTE=None

Change-Id: Ia6e4f54b1baaca323adf1bfc6cd1311fc02403cd
Reviewed-on: https://cos-review.googlesource.com/c/cos/overlays/board-overlays/+/14670
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
1 file changed