drm/nouveau/gr/gf100-: call FECS WFI_GOLDEN_SAVE method

This won't work on Ampere, and, it's questionable whether we should have
been using our FW's method of storing the golden context image with NV's
firmware to begin with.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>