drm/nouveau/subdev: add a pfuse subdev v2

We will use this subdev to disable temperature reading on cards that did not
get a sensor calibration in the factory.

v2:
- rename "nouveau_fuse_rd32" to "gxXXX_fuse_rd32" as adviced by Christian Costa
- fold the code a little as adviced by Emil Velikov

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