drm/amd/display: fix pipe re-assignment when odm present

Currently pipe split may steal an existing ODM pipe depending on stream
sequence. This change prevents that from happening as easily.

Signed-off-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Reviewed-by: Gary Kattan <Gary.Kattan@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>