drm/nouveau/nvif: simplify and tidy library interfaces

A variety of tweaks to the NVIF library interfaces, mostly ripping out
things that turned out to be not so useful.

- Removed refcounting from nvif_object, callers are expected to not be
  stupid instead.
- nvif_client is directly reachable from anything derived from nvif_object,
  removing the need for heuristics to locate it
- _new() versions of interfaces, that allocate memory for the object
  they construct, have been removed.  The vast majority of callers used
  the embedded _init() interfaces.
- No longer storing constructor arguments (and the data returned from
  nvkm) inside nvif_object, it's more or less unused and just wastes
  memory.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nv04_fence.c

@@ -57,7 +57,7 @@ nv04_fence_sync(struct nouveau_fence *fence,
 static u32
 nv04_fence_read(struct nouveau_channel *chan)
 {
-	struct nvkm_fifo_chan *fifo = nvxx_fifo_chan(chan);;
+	struct nvkm_fifo_chan *fifo = nvxx_fifo_chan(&chan->user);
 	return atomic_read(&fifo->refcnt);
 }