[Why]
Failing mode validation during dc_commit, leading to blackscreen with an
8k DP2 display during mode change.

[What]
Fix mixmatch between pipe and stream, which prevented us from
recognizing the link as DP2.
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Dmytro Laktyushkin <dmytro.laktyushkin@amd.com>
Acked-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Gabe Teeger <gabe.teeger@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>