drm/amd/display: Added root clock optimization flags

[Why & How]
Added root clock optimization debug flags for future debugging.

Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Solomon Chiu <solomon.chiu@amd.com>
Signed-off-by: Jake Wang <haonan.wang2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>