drm/nouveau/devinit/gf100: make devinit on resume safer

In case of successful suspend, devinit will have to be run and this is
the behavior currently hardcoded. However, as FD bug 94725 suggests,
there might be cases where runtime suspend leaves the GPU powered, and
in such cases devinit should not be run on resume.

On GF100+ we have a reliable way to know whether we need to run devinit.
Use it instead of blindly trusting the flag set by nvkm_devinit_fini().

The code around the NvForcePost also needs to be slightly reworked in
order to keep working.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Suggested-by: Dave Airlie <airlied@redhat.com>
Suggested-by: Karol Herbst <nouveau@karolherbst.de>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>