drm/amd/display: check cursor scaling

Don't allow user-space to set different scaling parameters for the
cursor plane and for the primary plane. Because of DCE/DCN design,
it's not possible to have a mismatch.

The old check in dm_update_plane_state is superseded by this new
check.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Simon Ser <contact@emersion.fr>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Harry Wentland <hwentlan@amd.com>
Cc: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>