drm/amd/display: Only use ODM2:1 policy for high pixel rate displays

We only gain a benefit of using the ODM2:1 dynamic policy if it allow us
to decrease DISPCLK to use the VMIN freq.  If the display config can
already achieve VMIN DISPCLK freq without ODM2:1, don't apply the
policy.

Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>