drm/amd/display: initialize lttpr

[Description]
When reading link, update the procedure as follows:
1-Set aux timeout to extended: 3.2ms
2-Start with reading lttpr caps
3-Determine if lttpr support should be enabled. Reset aux timeout to
400us if no repeater is found.

Signed-off-by: abdoulaye berthe <abdoulaye.berthe@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>