cros_bundle_firmware: Use sign_nv_cbootimage instead of nv_pkc_signing

CQ-DEPEND=CL:325370, CL:325381
BUG=chrome-os-partner:43018
BRANCH=None
TEST=Verified that signed image boots on dev-fused system

Change-Id: I51cc4e828b73ec66cc05407d31087fba0d722c7c
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://chromium-review.googlesource.com/325382
Trybot-Ready: Furquan Shaikh <furquan@chromium.org>
Tested-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Furquan Shaikh <furquan@chromium.org>
1 file changed