drm/nvd0/disp: add support for page flipping

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

diff --cc drivers/gpu/drm/nouveau/nouveau_display.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/nouveau_drv.h
Simple merge

diff --cc drivers/gpu/drm/nouveau/nouveau_object.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/nouveau_state.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/nvd0_display.c
Simple merge