Revert "drm/amdgpu/display: change pipe policy for DCN 2.0"

This reverts commit bcfab8e3

.

Hopefully this is fixed by the previous patch to enable
TEMP_DEPENDENT_VMIN for navi1x or otherwise and we can re-enable
MPC_SPLIT_DYNAMIC for DCN 2.0 for better power savings.

Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>