drm/nouveau/secboot: remove fixup_hs_desc hook

This hook can be removed if the function writing the HS
descriptor is aware of WPR settings. Let's do that as it allows us to
make the ACR descriptor structure private and save some code.

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