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: 3c7623fb ("drm/hisilicon/hibmc: Enable this hot plug detect of irq feature")
Signed-off-by: Baihan Li <libaihan@huawei.com>
Signed-off-by: Yongbang Shi <shiyongbang@huawei.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250813094238.3722345-8-shiyongbang@huawei.com


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>