drm/amd/display: Change blackout time to 0 on CZ/ST

These should only be non-0 if big hammer w/a is implemented. Currently
DC doesn't implement it, so leave them 0.

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>