drm/nouveau: hide sysfs pstate file behind an option again

No-one has yet had time to move this to debugfs as discussed during
the last merge window.  Until this happens, hide the option to make
it clear it's not going to be here forever.
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_sysfs.c

@@ -28,6 +28,10 @@
 
 #include "nouveau_sysfs.h"
 
+MODULE_PARM_DESC(pstate, "enable sysfs pstate file, which will be moved in the future");
+static int nouveau_pstate;
+module_param_named(pstate, nouveau_pstate, int, 0400);
+
 static inline struct drm_device *
 drm_device(struct device *d)
 {
@@ -160,7 +164,7 @@ nouveau_sysfs_fini(struct drm_device *dev)
 	struct nouveau_drm *drm = nouveau_drm(dev);
 	struct nvif_device *device = &drm->device;
 
-	if (sysfs->ctrl.priv) {
+	if (sysfs && sysfs->ctrl.priv) {
 		device_remove_file(nv_device_base(nvkm_device(device)), &dev_attr_pstate);
 		nvif_object_fini(&sysfs->ctrl);
 	}
@@ -177,6 +181,9 @@ nouveau_sysfs_init(struct drm_device *dev)
 	struct nouveau_sysfs *sysfs;
 	int ret;
 
+	if (!nouveau_pstate)
+		return 0;
+
 	sysfs = drm->sysfs = kzalloc(sizeof(*sysfs), GFP_KERNEL);
 	if (!sysfs)
 		return -ENOMEM;