drm/hisilicon: Enable the shadowfb for hibmc

set the prefer_shadow as 1,so we use the shadowfb to acceleration.
Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Signed-off-by: Gong junjie <gongjunjie2@huawei.com>
Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1578712146-16327-1-git-send-email-tiantao6@hisilicon.com

drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_drv.c

@@ -95,7 +95,7 @@ static int hibmc_kms_init(struct hibmc_drm_private *priv)
 
 	priv->dev->mode_config.fb_base = priv->fb_base;
 	priv->dev->mode_config.preferred_depth = 24;
-	priv->dev->mode_config.prefer_shadow = 0;
+	priv->dev->mode_config.prefer_shadow = 1;
 
 	priv->dev->mode_config.funcs = (void *)&hibmc_mode_funcs;