drm/amd/display: Revert "not disable dtb as dto src at dpms off"

[why]
not all the asic using the same code path.
need to revisit and limit the impact.

This reverts commit 32be4e39.

Reviewed-by: Gabe Teeger <gabe.teeger@amd.com>
Signed-off-by: Charlene Liu <Charlene.Liu@amd.com>
Signed-off-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Tested-by: Mark Broadworth <mark.broadworth@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>