drm/amd/display: do not change pipe split policy for RV2

[Why]
RV2 do not change pipe split policy in the
minimal pipe split transition state.
This will unblock mode support on some
parts that limit to DPM0 for power reason.

[How]
Do not change pipe split policy in the
minimal pipe split transition state to
allow 4k multi display configs to be
supported at DPM0.

Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Brian Chang <Brian.Chang@amd.com>
Signed-off-by: Derek Lai <Derek.Lai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>