drm/amd/display: Account for MPO planes in dcn32 mall alloc calculations

[WHY?]
Cannot only consider the MALL required from top pipes because of the MPO
case.

[HOW?]
Only count a pipe if it fits the following criteria:
1) does not have a top pipe (is the topmost pipe for that plane)
2) it does have a top pipe, but that pipe is associated with a different
   plane

Tested-by: Daniel Wheeler <Daniel.Wheeler@amd.com>
Reviewed-by: Nevenko Stupar <Nevenko.Stupar@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Dillon Varone <Dillon.Varone@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>