drm/amd/display: Refine condition of cursor visibility for pipe-split

[Why]
In some scenarios like fullscreen game, major plane is scaled. Then
if a upper layer owns the cursor, cursor is invisiable in the
majority of the screen.

[How]
Instead assuming upper plane handles cursor, summing up upper
split planes on the same layer. If whole upper plane covers current
half/whole pipe plane, disable cursor.

Reviewed-by: Krunoslav Kovac <Krunoslav.Kovac@amd.com>
Acked-by: Mikita Lipski <mikita.lipski@amd.com>
Signed-off-by: Dale Zhao <dale.zhao@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>