drm/amd/display: Add fallback defaults for invalid LTTPR DPCD caps

[WHY]
Some sinks are observed to return invalid LTTPR revision and/or invalid
LTTPR link rate capabilities.

[HOW]
Assume any LTTPR which reports invalid max link rate supports HBR3.
Don't validate LTTPR DPCD revision in dp_is_lttpr_present check.

Reviewed-by: George Shen <george.shen@amd.com>
Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>