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

Fixes hangs on driver load with multiple displays on
DCN 2.0 parts.

Bug: https://bugzilla.kernel.org/show_bug.cgi?id=215511
Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1877
Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1886
Fixes: ee2698cf

 ("drm/amd/display: Changed pipe split policy to allow for multi-display pipe split")
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org