drm/qxl: use QXL_GEM_DOMAIN_SURFACE for shadow bo.

The shadow bo is used as qxl surface, so allocate it as
QXL_GEM_DOMAIN_SURFACE.  Should usually be allocated in
PRIV ttm domain then, so this reduces VRAM memory pressure.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Acked-by: NNoralf Trønnes <noralf@tronnes.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20190118122020.27596-9-kraxel@redhat.com

drivers/gpu/drm/qxl/qxl_display.c

@@ -758,7 +758,7 @@ static int qxl_plane_prepare_fb(struct drm_plane *plane,
 			user_bo->shadow = old_bo->shadow;
 		} else {
 			qxl_bo_create(qdev, user_bo->gem_base.size,
-				      true, true, QXL_GEM_DOMAIN_VRAM, NULL,
+				      true, true, QXL_GEM_DOMAIN_SURFACE, NULL,
 				      &user_bo->shadow);
 		}
 	}