drm/amd/display: Use a temporary copy of the current state when updating DSC config

[why]
When updating DSC config, a new config has to be validated before proceeding
with applying the update. Validation, however, modifies the current state.
This means DSC config validation would affect pipe re-assignment, causing
intermittent screen corruption issues when ODM is required for DSC.

[how]
- Use a copy of the current state for modified DSC config validation
- Set the update type to FULL_UPDATE to correctly validate and set the
  actual state used for committing the streams

Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>