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: Austin Zheng <austin.zheng@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Signed-off-by: Tom Chung <chiahsuan.chung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>