drm/amd/display: update cur_lane_setting to an array one for each lane

[why]
To support per lane lane setting adjustment, we need to change cur_lane_setting
to an array one for each lane as the first step.

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>