drm/radeon/kms: although LVDS might be possible on crtc 1 don't do it.

LVDS always requests RMX_FULL, we need to fix it so that doesn't happen
before we can enable LVDS on crtc 1.
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_legacy_encoders.c

@@ -1066,6 +1066,7 @@ radeon_add_legacy_encoder(struct drm_device *dev, uint32_t encoder_id, uint32_t
 
 	switch (radeon_encoder->encoder_id) {
 	case ENCODER_OBJECT_ID_INTERNAL_LVDS:
+		encoder->possible_crtcs = 0x1;
 		drm_encoder_init(dev, encoder, &radeon_legacy_lvds_enc_funcs, DRM_MODE_ENCODER_LVDS);
 		drm_encoder_helper_add(encoder, &radeon_legacy_lvds_helper_funcs);
 		if (rdev->is_atom_bios)