drm/nouveau/secboot/tegra: Enable gp20b/gp10b firmware tag when relevant

This allows to have the related MODULE_FIRMWARE tag only
on relevant arch (arm64).
This will saves about 400k on initramfs when not relevant

Signed-off-by: Nicolas Chauvet <kwizart@gmail.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>