drm/amd/display: Enable DCN42 PMO policy

drm/amd/display: Enable DCN42 PMO policy

[Why]
The MinTTU policy in DML2.1 does not guarantee that we support p-state
in blank. This is a delta vs dml2 and earlier revisions as the prefetch
mode override has been removed in favor of a more configurable pstate
optimizer.

[How]
The policy has been added in a prior patch, this patch enables it based
on pmo flag.

Reviewed-by: Dillon Varone <Dillon.Varone@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Ivan Lipski <ivan.lipski@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>