drm/nouveau/therm/gp100: initial implementation of new gp1xx temperature sensor

v2:
 - add nv138 and drop nv13b chipsets (Ilia Mirkin)
 - refactor out status variable and instead mask tsensor (Ilia Mirkin)
 - switch SHADOWed state message away from nvkm_error() (Ilia Mirkin)
 - rename internal temperature variable (Karol Herbst)

v3:
 - use nvkm_trace() for SHADOWed state message (Ben Skeggs)

Signed-off-by: Rhys Kidd <rhyskidd@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>