drm/nouveau/therm: split the nv50 and nv84 code

This is needed because temperature management on nv50 can be enabled and it
looks about the same as nv40.

Signed-off-by: Martin Peres <martin.peres@labri.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
9 files changed