drm/amd/display: Update scaling settings on modeset

[Why]
We update scaling settings when scaling mode has been changed.
However when changing mode from native resolution the scaling mode previously
set gets ignored.

[How]
Perform scaling settings update on modeset.

Signed-off-by: Roman Li <roman.li@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Stylon Wang <stylon.wang@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>