drm/nouveau/secboot: add lazy-bootstrap flag

When the PMU firmware is present, the falcons it manages need to have
the lazy-bootstrap flag of their WPR header set so the ACR does not boot
them. Add support for this.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>