drm/amd/display: Enable DSC power-gating for DSC streams

[why]
Currently DSC power gating is disabled by default because the power
transition doesn't happen, causing a crash on some systems

[how]
Fix the lack of power state transition and enable DSC power gating
by default.

Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Reviewed-by: Martin Leung <Martin.Leung@amd.com>
Reviewed-by: Nevenko Stupar <Nevenko.Stupar@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>