drm/nouveau/gr: directly use instmem where currently possible

drivers/gpu/drm/nouveau/nvkm/engine/gr/ctxgf100.c

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

drivers/gpu/drm/nouveau/nvkm/engine/gr/gf100.h

drivers/gpu/drm/nouveau/nvkm/engine/gr/gk104.c

drivers/gpu/drm/nouveau/nvkm/engine/gr/gk20a.c

drivers/gpu/drm/nouveau/nvkm/engine/gr/gm107.c

drivers/gpu/drm/nouveau/nvkm/engine/gr/gm204.c

drivers/gpu/drm/nouveau/nvkm/engine/gr/nv20.c

drivers/gpu/drm/nouveau/nvkm/engine/gr/nv20.h

drivers/gpu/drm/nouveau/nvkm/engine/gr/nv25.c

drivers/gpu/drm/nouveau/nvkm/engine/gr/nv2a.c

drivers/gpu/drm/nouveau/nvkm/engine/gr/nv30.c

drivers/gpu/drm/nouveau/nvkm/engine/gr/nv34.c

drivers/gpu/drm/nouveau/nvkm/engine/gr/nv35.c

drivers/gpu/drm/nouveau/nvkm/subdev/mmu/base.c