drm/amd/display: Calculate scaling ratios on every medium/full update

[Why]
If a plane isn't being actively enabled or disabled then DC won't
always recalculate scaling rects and ratios for the primary plane.

This results in only a partial or corrupted rect being displayed on
the screen instead of scaling to fit the screen.

[How]
Add back the logic to recalculate the scaling rects into
dc_commit_updates_for_stream since this is the expected place to
do it in DC.

This was previously removed a few years ago to fix an underscan issue
but underscan is still functional now with this change - and it should
be, since this is only updating to the latest plane state getting passed
in.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>