drm: Kill ctx_count from struct drm_device

The only user of ctx_count is the via driver, and we can replace that
use with list_is_singular().

Signed-off-by: Ville Syrjälä <[e-mail]>
Reviewed-by: Daniel Vetter <[e-mail]>
Reviewed-by: Alex Deucher <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/drm_context.c

···
 
 	mutex_lock(&dev->ctxlist_mutex);
 	list_add(&ctx_entry->head, &dev->ctxlist);
-	++dev->ctx_count;
 	mutex_unlock(&dev->ctxlist_mutex);
 
 	return 0;
···
 			if (pos->handle == ctx->handle) {
 				list_del(&pos->head);
 				kfree(pos);
-				--dev->ctx_count;
 			}
 		}
 	}

drivers/gpu/drm/drm_fops.c

···
 
 				list_del(&pos->head);
 				kfree(pos);
-				--dev->ctx_count;
 			}
 		}
 	}

drivers/gpu/drm/via/via_mm.c

···
 
 	/* Linux specific until context tracking code gets ported to BSD */
 	/* Last context, perform cleanup */
-	if (dev->ctx_count == 1 && dev->dev_private) {
+	if (list_is_singular(&dev->ctxlist) && dev->dev_private) {
 		DRM_DEBUG("Last Context\n");
 		drm_irq_uninstall(dev);
 		via_cleanup_futex(dev_priv);

include/drm/drmP.h

···
 	/** \name Context handle management */
 	/*@{ */
 	struct list_head ctxlist;	/**< Linked list of context handles */
-	int ctx_count;			/**< Number of context handles */
 	struct mutex ctxlist_mutex;	/**< For ctxlist */
 
 	struct idr ctx_idr;