drm/amd/display: Fix calculation of virtual channel payload

[why]
The calculation of virtual channel payload would not take link settings
in account. As we calculate VCPI slots needed both PBN for stream and
also PBN per time slot.  Before we would use generic PBN per time slot,
which would not change with link settings causing wrong Payload
allocation.

[how]
Provide PBN per time slot for each Virtual channel payload calculation.

Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>