drm/i915: remove modeset reset from i915_reset

On gen4+ we don't reset the display unit, so resetting the complete
modeset state should not be necessary.

We can't do reset on gen3 anyway, which leaves us with gen2 reset:
According to Chris Wilson, that doesn't work so great, so he suggested
we just ignore that. If the need ever arrises, we can re-add it later
on.
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.c

@@ -904,21 +904,11 @@ int i915_reset(struct drm_device *dev)
 			intel_modeset_init_hw(dev);
 
 		drm_irq_uninstall(dev);
-		drm_mode_config_reset(dev);
 		drm_irq_install(dev);
 	} else {
 		mutex_unlock(&dev->struct_mutex);
 	}
 
-	/*
-	 * Perform a full modeset as on later generations, e.g. Ironlake, we may
-	 * need to retrain the display link and cannot just restore the register
-	 * values.
-	 */
-	mutex_lock(&dev->mode_config.mutex);
-	drm_helper_resume_force_mode(dev);
-	mutex_unlock(&dev->mode_config.mutex);
-
 	return 0;
 }