drm/amd/display: Cursor flicker when entering PSRSU

[Why]
The DAL driver may transmit the wrong cursor position to PSRSU
DMUB driver when there are multiple planes.

[How]
Currently the driver apply the HW cursor on the top plane. So we
should only transmit the cursor position on the top plane to
PSRSU DMUB driver.

Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Brian Chang <Brian.Chang@amd.com>
Signed-off-by: Robin Chen <po-tchen@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>