drm/nv40/gr: move to exec engine interfaces

Like nv50, this needs a good cleanup.

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

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

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

diff --cc drivers/gpu/drm/nouveau/nv40_graph.c
Simple merge