drm/nouveau/dma: split user classes out from engine implementations

drivers/gpu/drm/nouveau/include/nvkm/core/device.h

drivers/gpu/drm/nouveau/include/nvkm/engine/dma.h

drivers/gpu/drm/nouveau/nvkm/engine/Kbuild

drivers/gpu/drm/nouveau/nvkm/engine/device/priv.h

drivers/gpu/drm/nouveau/nvkm/engine/device/user.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/nv50.c

drivers/gpu/drm/nouveau/nvkm/engine/dma/Kbuild

drivers/gpu/drm/nouveau/nvkm/engine/dma/base.c

drivers/gpu/drm/nouveau/nvkm/engine/dma/gf100.c

drivers/gpu/drm/nouveau/nvkm/engine/dma/gf110.c

drivers/gpu/drm/nouveau/nvkm/engine/dma/nv04.c

drivers/gpu/drm/nouveau/nvkm/engine/dma/nv50.c

drivers/gpu/drm/nouveau/nvkm/engine/dma/priv.h

drivers/gpu/drm/nouveau/nvkm/engine/dma/user.c

drivers/gpu/drm/nouveau/nvkm/engine/dma/user.h

drivers/gpu/drm/nouveau/nvkm/engine/dma/usergf100.c

drivers/gpu/drm/nouveau/nvkm/engine/dma/usergf110.c

drivers/gpu/drm/nouveau/nvkm/engine/dma/usernv04.c

drivers/gpu/drm/nouveau/nvkm/engine/dma/usernv50.c

drivers/gpu/drm/nouveau/nvkm/engine/dmaobj/Kbuild