drm/nvc0/gr: add support for nvcf chipset

untested, written from a trace, accel disabled by default until it is

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nvc0_graph.c b/drivers/gpu/drm/nouveau/nvc0_graph.c
index 5b2f6f4..84321640 100644
--- a/drivers/gpu/drm/nouveau/nvc0_graph.c
+++ b/drivers/gpu/drm/nouveau/nvc0_graph.c
@@ -864,6 +864,9 @@
 	case 0xce: /* 4/4/0/0, 4 */
 		priv->magic_not_rop_nr = 0x03;
 		break;
+	case 0xcf: /* 4/0/0/0, 3 */
+		priv->magic_not_rop_nr = 0x03;
+		break;
 	}
 
 	if (!priv->magic_not_rop_nr) {