drm/nouveau/debugfs: Wake up GPU before doing any reclocking

Fixes various reclocking related issues on prime systems.

Signed-off-by: Karol Herbst <karolherbst@gmail.com>
Signed-off-by: Martin Peres <martin.peres@free.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>