drm/amd/display: Fix handling of scaling and underscan.

Summury of changes:

1: Both in check and commit Connector properties were handled as
   part of for_each(crtc) loop while they shoud have been handled
   in a dedicated for_each(connector)
   loop since they are connector properties. Moved.

2: Removed hacky plane add in amdgpu_dm_connector_atomic_set_property
   to force iteration on plane forconnector property. This was
   causing double call to commit_surface_for_stream both in crtc loop
   and plane loop.
3: Remove middleman DC interface and  call dc_commit_surfaces_to_stream
   directly to increase code clarity.

Remove it from atomic_commit.

Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>