drm/amd/display: Set LTTPR mode to non-LTTPR if no repeaters found

[WHY]
If no repeaters are found, we do not need or want to attempt to
link-train repeaters, as this could cause bugs.

Signed-off-by: Wesley Chalmers <Wesley.Chalmers@amd.com>
Acked-by: Bindu Ramamurthy <bindur12@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>