drm/amd/display: add dp dto programming function to dccg

[WHY&HOW]
Add support for programming dp dto via dccg.

Reviewed-by: Jun Lei <jun.lei@amd.com>
Acked-by: Stylon Wang <stylon.wang@amd.com>
Signed-off-by: Dillon Varone <dillon.varone@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>