drm: Return -EOPNOTSUPP in drm_setclientcap() when driver do not support KMS

All DRM_CLIENT capabilities are tied to KMS support, so returning
-EOPNOTSUPP when KMS is not supported.

v2: returning -EOPNOTSUPP(same value as posix ENOTSUP and available
in uapi) instead of -ENOTSUPP

v3: adding comments about the feature requirement about capabilities

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180918174809.17123-1-jose.souza@intel.com

drivers/gpu/drm/drm_ioctl.c

@@ -306,6 +306,12 @@ drm_setclientcap(struct drm_device *dev, void *data, struct drm_file *file_priv)
 {
 	struct drm_set_client_cap *req = data;
 
+	/* No render-only settable capabilities for now */
+
+	/* Below caps that only works with KMS drivers */
+	if (!drm_core_check_feature(dev, DRIVER_MODESET))
+		return -EOPNOTSUPP;
+
 	switch (req->capability) {
 	case DRM_CLIENT_CAP_STEREO_3D:
 		if (req->value > 1)