drm/nouveau: wake up the card if necessary during gem callbacks

The failure paths if we fail to wake the card are less than desirable,
but there's not really a graceful way to handle this case currently.

I'll keep this situation in mind when I get to fixing other vm-related
issues.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

diff --cc drivers/gpu/drm/nouveau/nouveau_gem.c
Simple merge