drm/amd/display: use previous aux timeout val if no repeater.

[Why]
The aux timeout value is not default before reading link cap.
Setting it to default when lttpr is not enabled causes some monitor
not to light up.

[How]
Read the aux engine timeout value before setting it to extended.
Set the aux engine timeout to its previous value if no lttpr.

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>