drm/nouveau/fb: initialise vram controller as pfb sub-object

drivers/gpu/drm/nouveau/Makefile

drivers/gpu/drm/nouveau/core/engine/fifo/nv40.c

drivers/gpu/drm/nouveau/core/include/subdev/fb.h

drivers/gpu/drm/nouveau/core/subdev/fb/base.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv04.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv10.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv1a.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv20.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv25.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv30.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv35.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv36.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv40.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv41.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv44.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv46.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv47.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv49.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv4e.c

drivers/gpu/drm/nouveau/core/subdev/fb/nv50.c