drm/nouveau/therm: rework thermal table parsing

As an accident, it should also fix temperature reading on nv4x.

v2: introduce nvbios_therm_entry as advised by darktama

Signed-off-by: Martin Peres <martin.peres@labri.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nouveau_pm.c b/drivers/gpu/drm/nouveau/nouveau_pm.c
index d2f2de6..bdd5095 100644
--- a/drivers/gpu/drm/nouveau/nouveau_pm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_pm.c
@@ -891,10 +891,7 @@
 		}
 		pm->voltage_get = nouveau_voltage_gpio_get;
 		pm->voltage_set = nouveau_voltage_gpio_set;
-		if (device->chipset == 0x50)
-			pm->temp_get = nv40_temp_get;
-		else
-			pm->temp_get = nv84_temp_get;
+		pm->temp_get = nv84_temp_get;
 		pm->pwm_get = nv50_pm_pwm_get;
 		pm->pwm_set = nv50_pm_pwm_set;
 	} else