drm/hisilicon/hibmc: fix dp and vga cannot show together

If VGA and DP connected together, there will be only one can get crtc.
Add encoder possible_clones to support two connectors enable.

Fixes: 3c7623fb5bb6 ("drm/hisilicon/hibmc: Enable this hot plug detect of irq feature")
Signed-off-by: Baihan Li <[e-mail]>
Signed-off-by: Yongbang Shi <[e-mail]>
Reviewed-by: Dmitry Baryshkov <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Baryshkov <[e-mail]>

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

···
 static int hibmc_kms_init(struct hibmc_drm_private *priv)
 {
 	struct drm_device *dev = &priv->dev;
+	struct drm_encoder *encoder;
+	u32 clone_mask = 0;
 	int ret;
 
 	ret = drmm_mode_config_init(dev);
···
 		drm_err(dev, "failed to init vdac: %d\n", ret);
 		return ret;
 	}
+
+	drm_for_each_encoder(encoder, dev)
+		clone_mask |= drm_encoder_mask(encoder);
+
+	drm_for_each_encoder(encoder, dev)
+		encoder->possible_clones = clone_mask;
 
 	return 0;
 }