drm/amd/display: apply vmin optimization even if it doesn't reach vmin level

[why]
Based on power measurement result, in most cases when display clock is higher
than Vmin display clock, lowering display clock using dynamic ODM will improve
overall power consumption by 0 to 4 watts even if we can't reach Vmin.

[how]
Allow vmin optimization applied even if dispclk can't reach Vmin.

Reviewed-by: Jun Lei <jun.lei@amd.com>
Signed-off-by: Jerry Zuo <jerry.zuo@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>