drm/amd/display: Update cursor offload assignments

drm/amd/display: Update cursor offload assignments

[Why & How]
- Cursor lines per chunk must be assigned from hubp->att and not
  hubp->pos (the one in hubp->pos is unassigned)
- In DCN401 DPP, cur0_enable in attribute struct must be assigned
  as this is the field passed to DMU
- DCN401 should not program position in driver if offload is enabled

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>