drm/amd/display: Fix Mode Cutoff in DSC Passthrough to DP2.1 Monitor

Source --> DP2.1 MST hub --> DP1.4/2.1 monitor

When change from DP1.4 to DP2.1 from monitor manual, modes higher than
4k120 are all cutoff by mode validation. Switch back to DP1.4 gets all
the modes up to 4k240 available to be enabled by dsc passthrough.

[why]
Compared to DP1.4 link from hub to monitor, DP2.1 link has larger
full_pbn value that causes overflow in the process of doing conversion
from pbn to kbps.

[how]
Change the data type accordingly to fit into the data limit during
conversion calculation.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>