drm/nouveau/secboot: support standard NVIDIA HS binaries

I had the brilliant idea to "improve" the binary format by removing
a useless indirection in the HS binary files. In the end it just
makes things more complicated than they ought to be as NVIDIA-provided
files need to be adapted. Since the format used can be identified by the
header, support both.

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