drm/amd/display: Assume active upper layer owns the HW cursor

[why]
The current logic checks if there's an upper pipe whose viewport
completely covers the current pipe viewport.
This fails in pipe splitting case as you can have layer 1 pipe that
crosses the two layer 0 pipes where it's contained in both, but neither
covers it completely, hence we allow the cursor on both layers.

[How]
Instead of trying to "sum up" rectangles from the higher level pipes
which could leave gaps and would not work generically, we will assume if
there's an upper layer that is active, it will control the HW cursor.

Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Krunoslav Kovac <Krunoslav.Kovac@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>