drm: Unamp the entire device address space on device unplug

Invalidate all BOs CPU mappings once device is removed.

v3: Move the code from TTM into drm_dev_unplug
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/414809/Signed-off-by: Christian König <christian.koenig@amd.com>

drivers/gpu/drm/drm_drv.c

@@ -469,6 +469,9 @@ void drm_dev_unplug(struct drm_device *dev)
 	synchronize_srcu(&drm_unplug_srcu);
 
 	drm_dev_unregister(dev);
+
+	/* Clear all CPU mappings pointing to this device */
+	unmap_mapping_range(dev->anon_inode->i_mapping, 0, 0, 1);
 }
 EXPORT_SYMBOL(drm_dev_unplug);