drm/nouveau/sw: turn flip completion into an event

drivers/gpu/drm/nouveau/include/nvif/class.h

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

drivers/gpu/drm/nouveau/nouveau_chan.c

drivers/gpu/drm/nouveau/nouveau_display.c

drivers/gpu/drm/nouveau/nouveau_drm.c

drivers/gpu/drm/nouveau/nouveau_drm.h

drivers/gpu/drm/nouveau/nouveau_fence.h

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

drivers/gpu/drm/nouveau/nvkm/engine/sw/chan.c

drivers/gpu/drm/nouveau/nvkm/engine/sw/chan.h

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

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

drivers/gpu/drm/nouveau/nvkm/engine/sw/nv10.c

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

drivers/gpu/drm/nouveau/nvkm/engine/sw/nv50.h

drivers/gpu/drm/nouveau/nvkm/engine/sw/nvsw.c

drivers/gpu/drm/nouveau/nvkm/engine/sw/nvsw.h

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