drm/amd/display: Fix screen tearing on vrr tests

[Why]
Screen tearing is present in tests when setting the frame rate to
certain fps

[How]
Revert previous optimizations for low frame rates.

Signed-off-by: Amanda Liu <amanda.liu@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>