drm/hisilicon/hibmc: fix rare monitors cannot display problem

drm/hisilicon/hibmc: fix rare monitors cannot display problem

[ Upstream commit 9f98b429ba67d430b873e06bcfb90afa22888978 ]

In some case, the dp link training success at 8.1Gbps, but the sink's
maximum supported rate is less than 8.1G. So change the default 8.1Gbps
link rate to the rate that reads from devices' capabilities.

Fixes: 54063d86e036 ("drm/hisilicon/hibmc: add dp link moduel in hibmc drivers")
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/20250813094238.3722345-6-shiyongbang@huawei.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>