drm/amd/display: Disable integerscaling for downscale and MPO

drm/amd/display: Disable integerscaling for downscale and MPO

[Why]
Integer scaling is applied to MPO planes when downscaling,
MPO planes use variable taps and integer scaling sets taps=1

[How]
Disable integer scaling on MPO planes,
Disable integer scaling for downscaling planes

Signed-off-by: Aidan Yang <Aidan.Yang@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>