drm/nouveau: don't detect DSM for non-NVIDIA device

The call site of nouveau_dsm_pci_probe() uses single set of output
variables for all invocations. So, we must not write anything to them
unless it's an NVIDIA device. Otherwise, if we are called with another
device after the NVIDIA device, we'll clober the result of the NVIDIA
device.

For example, if the other device doesn't have _PR3 resources, the
detection later would miss the presence of power resource support, and
the rest of the code will keep using Optimus DSM, breaking power
management for that machine.

Also, because we're detecting NVIDIA's DSM, it doesn't make sense to run
this detection on a non-NVIDIA device anyway. Thus, check at the
beginning of the detection code if this is an NVIDIA card, and just
return if it isn't.

This, together with commit d22915d2 ("drm/nouveau/devinit/tu102-:
wait for GFW_BOOT_PROGRESS == COMPLETED") developed independently and
landed earlier, fixes runtime power management of the NVIDIA card in
Lenovo Legion 5-15ARH05. Without this patch, the GPU resumption code
will "timeout", sometimes hanging userspace.

As a bonus, we'll also stop preventing _PR3 usage from the bridge for
unrelated devices, which is always nice, I guess.

Fixes: ccfc2d5c

 ("drm/nouveau: Use generic helper to check _PR3 presence")
Signed-off-by: Ratchanan Srirattanamet <peathot@hotmail.com>
Closes: https://gitlab.freedesktop.org/drm/nouveau/-/issues/79
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/DM6PR19MB2780805D4BE1E3F9B3AC96D0BC409@DM6PR19MB2780.namprd19.prod.outlook.com