drm/amd/display: disable lttpr for invalid lttpr caps.

1-Read lttpr caps in 5-bytes
2-Parse caps
3-Validate caps and set lttpr_mode
4-Use hw default timeout when lttpr is disabled.

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