sign_firmware: Add nv_pkc_signing step if required

If nv_pkc.pem file is present for a device, use nv_pkc_signing for
adding PKC signature in the firmware image.

BUG=chrome-os-partner:44227
BRANCH=None
TEST=unittests run fine. verified image boots on fused system.

Change-Id: I9b2f48da55137a0e4a75f23d16d3779be1aa94c8
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://chromium-review.googlesource.com/296452
Commit-Ready: Furquan Shaikh <furquan@chromium.org>
Tested-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
2 files changed