drm/amd/display: Refine condition for cursor visibility

drm/amd/display: Refine condition for cursor visibility

[why]
There's a special case where upper plane is not the main plane. If it owns
the cursor, it will be invisible in the majority of the screen.

[How]
The condition for disabling cursor is changed:
- check if upper viewport completely covers current. This was the
previous change that doesn't handle all scenarios with pipe splitting.
- if not, show the cursor only if it's not scaled or no upper pipe.

Reviewed-by: Aric Cyr <aric.cyr@amd.com>
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>