drm/nouveau/fb/gp102-: cache scrubber binary on first load

During system shutdown nouveau might not be able to request firmware from
Userspace, which then leads to a regression preventing the system from
shutting down.

Cache the scrubber binary for this case.

Fixes: 0e44c217 ("drm/nouveau/flcn: new code to load+boot simple HS FWs (VPR scrubber)")
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/CACAvsv7Uf5=K44y8YLsiy0aMnc1zvGEQdeDe7RQF=AV+fxxzuQ@mail.gmail.com